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A checklist of rheophytes of Cameroon
expand article infoFelix Kuetegue, Bonaventure Sonké§, Gabriel K. Ameka|
‡ University of Yaoundé I, Yaounde, Cameroon
§ International Joint Laboratory DYCOFAC, Yoaundé, Cameroon
| University of Ghana, Accra, Ghana
Open Access

Abstract

Rivers in Cameroon were surveyed to collect and document rheophytic plants. Rheophytes are the dominant aquatic macrophytes in tropical river systems, where they are adapted to extreme environments of rushing water (e.g., river rapids, waterfalls and flash floods). Rheophytic plants are useful indicators of river health. However, their habitats are threatened by human activities such as agriculture, plantation development, alluvial mining and dam construction, particularly in tropical countries. In this survey we documented 66 rheophytic species in 29 genera and 16 families. Two ferns, 8 monocotyledons and 56 dicotyledons were listed. Apart from the Podostemaceae family in which all species are rheophytic, the other 15 families have few species which are rheophytic. Five of these families have up to four species and the remaining 10 have only one member as a rheophytic species. The conservation status of each species is assessed and discussed. This work urges botanists, conservationists, and policy makers to do more to protect the habitats of rheophytes and put in place strategies and action plans for the conservation of this important biological group.

Keywords

Cameroon, conservation, distribution, inventory, Rheophyte diversity

Introduction

Rheophyte, a term coined by van Steenis in 1932 (van Steenis 1978), is used to describe an aquatic plant which is in nature restricted to swift-running rivers and streams and grows up to flood level, but not beyond the reach of regularly occurring flash floods (van Steenis 1978, 1981). Rheophytes occur worldwide but are found particularly in evergreen rain forests, where they are the dominant aquatic macrophytes in tropical river systems (van Steenis 1978, Quiroz et al. 1997, Ameka 2000, Hoyos-Gomez and Bernal 2018). Members of this biological group of plants are not necessarily taxonomically related, but they show a common adaptation to a restricted ecological habitat or environmental factors (van Steenis 1981, Ameka 2000, Ameka et al. 2002, Hoyos-Gomez and Bernal 2018). Rheophytes are adapted to extreme environments of rushing water by having lanceolate leaves, slender and flexible but tough stems, and strong usually fibrous, root systems (Hoyos-Gomez and Bernal 2018). These plants are generally perennial herbs or shrubs, sometimes small to medium trees, while few grow into tall trees. Two categories of rheophytes are recognized: (i) obligate and, (ii) facultative rheophytes (e.g., Ameka et al. (2002)). Obligate rheophytes are confined to waterfalls, streams and river-beds and banks, and below the flood level. Facultative types are found not only in river-beds but also occur in wet places where they are not subjected to fast-flowing water. In this work, rheophytic plants or rheophytes refer to obligate rheophytes.

Twenty-one rheophytic species, excluding the Podostemaceae, were recognized in tropical Africa, in a worldwide census of rheophytes by van Steenis (1981). Earlier in an assessment of rheophytic plants in South Africa, van Steenis (1978) recognized 7 species, again excluding the Podostemaceae. According to Ameka et al. (2002), in a survey of rivers, for rheophytes, in southern Ghana, from 1994 to 2000, 15 species including four Podostemaceae were recorded. Surprisingly, woody rheophytes were not encountered in the survey by Ameka et al. (2002) although van Steenis (1981) had earlier indicated that half of all rheophytes worldwide are woody. In their work on rheophytes of southern Ghana, Ameka et al. (2002) also reviewed rheophytes of Africa but relied only on records from the literature. Their review revealed that ca. 114 species including 73 Podostemaceae species were documented as rheophytes in Africa. Regarding distribution by country, Cameroon was reported to have 53 rheophytes including 33 Podostemaceae; South Africa 7 rheophytes and 3 Podostemaceae; and Nigeria 19 rheophytes including 4 Podostemaceae (Ameka et al. 2002). The known number of rheophytic plants recorded for Africa (including Cameroon, Ghana, Nigeria and South Africa) probably underestimates the actual number and reflects the degree of paucity of information, and lack of systematic collection effort of Podostemaceae and other rheophytic plants in African countries.

A survey to document and study the rheophytes of Cameroon is important for a number of reasons: (i) rheophytes are poorly known in tropical Africa, including Cameroon, compared to South East Asia and South America, according to van Steenis (1981), (ii) they are the dominant aquatic macrophytes in rivers; and are useful biological indicators of river health, and (iii) the diversity of rheophytes is threatened and some species are in danger of disappearing by the increased land-use practices adjoining the rivers, particularly for agriculture, plantation development, and illegal logging; and in the river courses for alluvial mining (e.g., gold and diamond), and also damming of rivers for hydropower in tropical countries. The construction of dams causes destruction of the habitats of rheophytes, particularly the Podostemaceae.

The survey to enumerate and document the rheophytes of Cameroon was conducted from 2010 to 2014; and the rheophytic species encountered are reported here. It is hoped that this work will stimulate further research on rheophytes across the rest of tropical Africa. We draw attention to the urgent need to stop the destruction of habitats of rheophytes and rather map out strategies and action plans for the conservation of this important biological group.

Materials and methods

The study site

A survey of rheophytes was carried out in Cameroon, situated between 2°–13°N and 9°–16°E (Fig. 1). Cameroon is generally divided into three main climatic zones: Equatorial climate zone, (2°–6°N), characterized by an annual average precipitation of 2000 mm, and an average temperature of about 25 °C; the Sudanese climate zone, (6°–10°N), characterized by 5–6 months of dry season with an average temperature of about 22 °C, and 1000 mm of precipitation; and the Sudano-Sahalian climate zone, (10°N–13°N), characterized by 7 months of dry season and 400–900 mm of precipitation (Olivry 1986, Munang et al. 2008). From north to south Cameroon, the vegetation ranges from steppe zone, savannah zone, and to forest zone.

The central and western parts of Cameroon are dominated by high mountains and plateaus (Segalen 1967, Suchel 1972, Ndoh et al. 2016). The high western range has peaks which vary in elevation e.g., Mt Etinde (1474 m), Mt Mwoanenguaba (2396 m), Mt Kupe (2050 m), Mt Bamboutos (2740 m) with the highest elevation at Mt Cameroon (4095 m) (Letouzey 1985, Cheek et al. 2004, Sainge 2017). The Adamawa or Central High plateau reaches up to 1500 m (Suchel 1972). Both the western range and the Central High plateau are the result of volcanic and tectonic activities giving rise to faults, volcanic cones and volcanic lakes. These two sectors constitute the main watersheds of Cameroon’s drainage systems. The southern section of the country is dominated by a plateau (500 to 900 m) which gently slopes to the east (Congo basin) but falls by steps to the Atlantic coast (Suchel 1972). While the far north is dominated by the lake Chad Basin (Suchel 1972, Olivry 1986), its southern fringe is the River Benue basin, both of which present a monotonous relief. The narrow coastal zone is marked by unstable swamps, especially from the Wouri-Moungo basins to the Ndian-Akpa-Yafe basins (Suchel 1972, Olivry 1986).

Figure 1. 

Map of Cameroon showing collecting localities of rheophytes.

Survey

In documenting the rheophytes of Cameroon, several rivers (Fig. 1) were visited during the dry season (November-February and July–August in the southern part of the country; and October–April in the northern part of the country). In the dry period, water levels recede in rivers and the majority of plants are in their reproductive phase. Sections of the rivers with rocky substrate were intensively sampled. The rheophytic status of some species were in doubt, particularly those on river banks and edge of rivers, such species and their localities were visited also during the wet season (March –June and July–October in the southern part of the country; May–September in the northern part of the country), when the water flow and level were high. This enabled us to determine whether a particular species is able to withstand spate, and is therefore rheophytic. Notes were taken on the habitat conditions, and characteristic rheophytic features of the species encountered, particularly the leaf shape and form, stem characteristics, and rooting system. Voucher specimens of each taxon collected were deposited in the Cameroon National Herbarium in Yaoundé (YA), [YA, acronym, Thiers (2017)]. Voucher specimens were not collected for every rheophyte species (particularly the Podostemaceae) encountered in the field. This is because such species were common and voucher specimens already exist for them. In cases where voucher specimens were not collected, notes were taken to indicate presence of the rheophytic species at the locality.

Voucher specimens in YA were also consulted for rheophytes already collected from Cameroon. The Flora of West Tropical Africa (Keay 1954, 1958, Hepper 1963, 1968, 1972) and other published works on rheophytes (e.g., van Steenis 1978, van Steenis 1981, Ameka et al. 1996, Ameka, et al. 2002), and from the study area (e.g., Hooper (1972), Duncan (1986), Cusset (1987), Cable and Cheek (1998), De Block (1998), Pollard and Paton (2001), Cheek et al. (2004), Brooks et al. (2011), Ghogue (2011), Onana and Cheek (2011), Cheek et al. (2017a), and Cheek et al. (in press)), were also referred to, and used to confirm the identification of rheophyte species collected, and in the compilation of a rheophytic checklist for Cameroon. In addition, the following websites were also consulted: http://www.worldchecklistofplants.org; http://www.ipni.org; http://www.plantlist.org; http://www.iucnredlist.org.

Distribution maps of rheophytes of Cameroon were done using georeferenced specimen data derived from specimen labels or available literature, and our own field surveys. The conservation status of each species was assessed by calculating the extent of occurrence (EOO) and the area of occupancy (AOO) in Cameroon using GeoCAT (Geospatial Conservation Assessment tool; Bachman et al. 2011) and applying The IUCN Red List Categories and Criteria, version 10.1 (IUCN 2013, IUCN Standards and Petitions Subcommittee 2017). The AOO was calculated based on a user defined grid cell of 2 km. The number of ‘locations’ (as defined by IUCN 2017) was calculated with regard to each particular threat, such that a single ‘location’ may encompass more than one adjacent subpopulation. The term subpopulation is used according to IUCN (2017). The Red Data Book of the Flowering Plants of Cameroon: IUCN Global Assessments (Onana and Cheek 2011), Ghogue (2011), and the online IUCN Red List (http://www.iucnredlist.org) were consulted while determining the conservation status of the species in this study. Our conservation assessments are yet to be submitted to IUCN and as such these assessments should be treated as “preliminary conservation assessments”.

Results

The list of rheophytes identified during the study is presented as a checklist organized by families, and each entry consists of the following:

  1. Species name, authority and place of publication
  2. Synonym(s) where applicable
  3. Type, followed by Basionym where applicable
  4. Description
  5. Specimens examined
  6. Habitat
  7. Distribution
  8. Conservation status in Cameroon

Checklist of rheophytes from Cameroon

The checklist of rheophytes of Cameroon contains 16 families and 66 species. The rheophytic species listed may be placed in two categories: in the first category are families in which few species are rheophytic and in the second category are families in which all species are rheophytic. The former category has 15 families, 17 genera, and 23 species, while the latter category contains only the Podostemaceae family with 12 genera and 43 species.

Families in which few species are rheophytic

Pteridophytes (ferns)

Lomariopsidaceae

Bolbitis fluviatilis (Hook.) Ching, Index Filic. Suppl. Tert. 48 (1934)

Acrostichum fluviatile Hook., Sp. Fil. 5: 274 (1864)

Acrostichum phanerodictyon Baker, Bol. Soc. Brot. 4: 156, t. 2 (1886)

Leptochilus fluviatilis (Hook.) C.Chr., Index Filic. 10, 385 (1905)

Type

Equatorial Guinea, Fernando Po (Bioko), G. Mann 442 (K, K000435773).

Description

Herbaceous, rhizome creeping, with opaque, castaneous scales; fixed to rocks by roots; sterile fronds lanceolate, up to 85 cm long; fertile fronds up to 90 cm long with sporangia on lower surface.

Specimens examined

15 km southeast of Zingui, 14 Mar 1968, R. Letouzey 9031 (YA); near Ababendoman, 65 km southeast of Ebolowa, 00 Jan 1970, R. Letouzey 9958 (YA); Muanenguba Mts. northeast of Nkongsamba, 4°58'N, 9°53'E, 11 Dec 1971, A. J. M. Leeuwenberg 8848 (YA).

Habitat

Rocky riverbeds and streams, and rocky borders of streams and rivers; in evergreen rainforest.

Distribution

Cameroon (Fig. 2), Democratic Republic of Congo, Gabon, Ghana, and Liberia.

Conservation status in Cameroon

Bolbitis fluviatilis is not listed on http://www.iucnredlist.org nor in Onana and Cheek (2011). The species is currently known from five localities. The extent of occurrence (EOO) is more than 20,000 km2, and the area of occupancy (AOO) is about 20 km2. Some collecting localities of the species are within the Cameroon Development Corporation (CDC) palm tree plantations, and other localities are proposed for plantation development. Based on this threat, extent and/or quality of the habitat of the species B. fluviatilis is here assessed as Endangered. IUCN Red List Category: Endangered ENB2ab (ii, iii).

Figures 2–10. 

2 Bolbitis fluviatilis (Hook.) Ching 3 Bolbitis heudelotii (Bory ex Fée) Alston 4 Lepidagathis alopecuroides R.Br. ex Griseb. 5 Achyranthes talbotii Hutch & Daziel 6 Crinum natans Baker 7 Kanahia laniflora (Forssk.) R.Br. 8 Anubias barteri Schott 9 Cyperus rheophyticus Lye 10 Cyperus tonkinensis C.B.Clarke var. baikiei (C.B.Clarke ex Kuk) S.S.Hooper.

Bolbitis heudelotii (Bory ex Fée) Alston, J. Bot. 72 (Suppl. 2): 3 (1934)

Gymnopteris heudelotii Bory ex Fée, Mém. Foug., 2. Hist. Acrostich. 84: 45, t. 45 (1845)

Leptochilus heudelotii (Bory ex Fée) C.Chr., Index Filic. 11, 385 (1905)

Type

Guinea Conakry, Fouta Djallon, in herb Bory, Heudelot 803 (holotype: P).

Description

Herbaceous, rhizome thick with dark brown scales and creeping on rocks; numerous roots; sterile fronds 30–80 cm long, linear to elliptical; fertile fronds 25–100 cm, long, linear, abaxial surface with sporangia.

Specimens examined

Pangar River, at Tapare (Dang Assoura), 5°22'N, 13°31'E, 11 Feb 1961, R. Letouzey 3452 (YA); Maan, 24 km southeast of Nyabesan, 00 Feb 1963, J. & A. Raynal 10264 (YA); East of Kribi on Kienke River, 2°56'N, 9°55'E, 05 Apr 1969, J. J. Bos 4282 (YA); Limbe at Limbe River, 4°2'N, 9°12'E, 13 Jan 2011, F. Kuetegue 412, 414 (YA).

Habitat

Riverbeds of perennial streams; edge of waterfalls; seasonally flooded in swift-flowing rivers or streams, able to withstand spate; in rainforest.

Distribution

Widespread in tropical Africa. Angola, Benin, Cameroon (Fig. 3), Central African Republic, Congo, Côte d’Ivoire, Democratic Republic of Congo, Ghana, Guinea, Malawi, Mali, Mozambique, Nigeria, Sierra Leone, Tanzania, Togo, Zambia, and Zimbabwe.

Conservation status in Cameroon

Bolbitis heudelotii is not listed on http://www.iucnredlist.org nor in Onana and Cheek (2011). The extent of occurrence of this species is about 102,900 km2 with an area of occupancy of about 32 km2. The species is currently known from 8 localities. The main pressures on the habitats are logging; dam construction (i.e. Lom-Pangar Hydro-electric dam, between Lom and Pangar) and expansion of cocoa farms. Based on these threats, extent and/or quality of habitat B. heudelotii is here assessed as Vulnerable. IUCN Red List Category: Vulnerable VUB2ab (ii, iii).

Acanthaceae

Lepidagathis alopecuroides R.Br. ex Griseb., Fl. Brit. W. I. 453 (1862)

Adenosma chenopodiifolia (Poir.) Spreng., Syst. Veg. ed. 16, 2: 829 (1825)

Aetheilema alopecuroidea (Vahl) Spreng., Syst. Veg. 2: 826 (1825)

Ruellia alopecuroidea Vahl, Eclog. Amer. 2: 49 (1798)

Ruellia chenopodiifolia Poir., Encycl. 6(1): 339 (1804)

Teliostachya alopecuroidea Nees, Prodr. 11: 263 (1847)

Type

Sierra Leone, by Scaries River, 1891, G. F. Scott Elliot 4533 (K, K000529239).

Description

Herb, slender, flexible, decumbent and branching stems, with lanceolate leaves 5.0–6.5 × 0.4–0.6 cm; strong fibrous root system; pink or purplish flowers.

Specimens examined

40 km northwest of Moloundou on Dja River, 18 Mar 1973, R. Letouzey 12132 (YA); Ndian 50 m on bank of Mana River, 4°58'N, 8°51'E, 09 Dec 1983, D. W. Thomas 2659 (YA); Mundemba on Mana River, 11 Jan 1998, M. Cheek 8850 (YA).

Habitat

Rocky and sandy riverbeds or on the banks of rivers and streams; in rainforest.

Distribution

Benin, Cameroon (Fig. 4), Côte d’Ivoire, Gabon, Ghana, Guinea and Nigeria.

Conservation status in Cameroon

Lepidagathis alopecuroides is not listed on http://www.iucnredlist.org nor in Onana and Cheek (2011). The extent of occurrence of this species is estimated at 124,600 km2 and has an area of occupancy of about 20 km2. The taxon is currently known from five localities. Construction of dams are in progress at two sites for this species: a hydroelectric dam at Natchigal on the Sanaga River; and another on the Dja River, and if fully operational the habitat of L. alopecuroides may be destroyed. Based on these threats, and the fact that the species is only known from five localities, L. alopecuroides is here assessed as Endangered. IUCN Red List Category: Endangered ENB2ab (ii, iii).

Amaranthaceae

Achyranthes talbotii Hutch. & Dalziel, Fl. W. Trop. Afr. 1: 127 (1927)

Type

Nigeria, Keay, R. W. J. FHIFHI 28284 (holotype: K, K000243718).

Description

Perennial herb with soft woody stem to 45 cm tall; strong fibrous root system; lanceolate leaves 2–4 × 1–1.5 cm.

Specimens examined

Near Ndokman II, approximately 8 km east of Yingui or 35 km east of Yabassi, 4°34'N, 10°10'E, 00 Jan 1972, R. Letouzey 10938 (YA); bank of Nkam River, near Sake, 3 km southwest of Nkondjok, 4°77'N, 10°17'E, 07 Jan 1972, R. Letouzey 11163 (YA); Mumgo River, Kumba-Loum road, 2°49'N, 9°33'E, 00 Jan 1981, Breyne 5062 (YA); Kombon at the bank of Kombon River, 4°59'N, 9°26'E, 23 Mar 2011, F. Kuetegue 316 (YA).

Habitat

Sandy and rocky riverbeds or up to flood level on the bank, in rainforest.

Distribution

Cameroon (Fig. 5) and Nigeria.

Conservation status in Cameroon

Achyranthes talbotii was assessed by Cheek (2014) globally as Near Threatened (NT) at http://www.iucnredlist.org. The species was, however, assessed by Onana and Cheek (2011) for Cameroon as Vulnerable, since at that time it was known from only 10 sites. The taxon is currently known from about 25 localities. The extent of occurrence is estimated to be above 20,000 km2 and the area of occupancy is about 100 km2. At some localities, road construction and arable farming are in progress but on a limited scale. Although the habitat of the species is under pressure, it does not appear to qualify as threatened under the IUCN red list criteria (IUCN 2013, 2017). While the expectation is that human pressure will increase the loss of habitat, and reduce the area of occupancy and extent of occurrence, it is not anticipated these threats will be significant. A. talbotii is here reassessed as of Least Concern. IUCN Red List Category: Least Concern (LC).

Amaryllidaceae

Crinum natans Baker., Fl. Trop. Afr. 7 (3): 396 (1898)

Crinum natans Baker subsp. inundatum Kwembeya & Nordal; Phylogeny Speciation Biogeogr. Crinum Chlorophytum 3:16 (2008)

Type

Equatorial Guinea, Fernando Po (Bioko), G. Mann 1416 (lectotype: K; isotype: P).

Description

Herb with small bulb, very strong root system; leaves crinkled, submerged and floating, 140 × 2.2 cm; flowers large, borne above the water.

Specimens examined

15 km north of Edea, near the bridge, 22 Jan 1969, J. J. Bos 1969 (YA); Balondo, 25 km southwest of Nkongsamba, 4°43'N, 9°51'E, 00 Mar 1976, R. Letouzey 14441 (YA); Soo village, near bridge on Soo River, 3°20'N, 11°30'E, 06 Apr 1977, Inger Nordal 906 (YA); Diongo (Kumba – Nguti road) on bank of Mengue River, 4°45'N, 9°29'E, 21 Mar 2011, F. Kuetegue 507 (YA).

Habitat

Bed of swift-flowing perennial streams and rivers, submerged permanently, strong fibrous root system, in sand, silt or gravel riverbeds; in evergreen rainforest.

Distribution

Cameroon (Fig. 6), Côte d’Ivoire, Gabon, Ghana, Guinea, Liberia, Nigeria, and Sierra Leone.

Conservation status in Cameroon

Crinum natans was not listed on http://www.iucnredlist.org nor assessed by Onana and Cheek (2011). The taxon is currently known from 10 localities. The extent of occurrence of C. natans is about 92,850 km2 and the area of occupancy is about 40 km2. Human activities at the localities include timber exploitation; and planned mining operations, hydroelectric dams and plantation development. Based on these threats, and the continuous decline of the vegetation cover in the area, extent and/or quality of its habitat, the species is here assessed as Vulnerable. IUCN Red List Category: Vulnerable VUB2ab (ii, iii).

Asclepiadaceae

Kanahia laniflora (Forssk.) R.Br., Voy. Abyss. App.: Ixiv (1814)

Asclepias coarctata S.More, J. Bot. 46: 297 (1908)

Asclepias fluviatilis A.Chev., Bull. Soc. Bot. France 61(8): 271 (1917)

Asclepias laniflora Forssk., Fl. Aegypt.-Arab. 51 (1775)

Asclepias rivalis S.More, J. Bot. 52: 337 (1914)

Gomphocarpus glaberrimus Oliv., Trans. Linn. Soc. London 29(3): 110 (1875)

Kanahia consimilis N.E.Br., Fl. Trop. Afr. 4(1.2): 298 (1902)

Kanahia glaberrima (Oliv.) N.E.Br., Fl. Trop. Afr. 4(1.2): 297 (1902)

Type

Cameroon, G. L. Bates 322 (lectotype: K, K000234855).

Description

Erect woody shrub, up to 2 m high; leaves linear-lanceolate 4–15 × 0.5–1.0 cm, glabrous; inflorescence axillary, one per node between leaf bases; flowers creamy white.

Specimens examined

Dibombe River, 4°41'N, 9°48'E, 16 Mar 1965, A. J. M. Leeuwenberg 9708 (YA); bank of UVE River, 20 km northwest of Kumba, 20 Mar 1976, R. Letouzey 38378 (YA); Mundemba, on Ndian (Mana) River, 4°58'N, 8°51'E, 09 Dec 1983, D. W. Thomas 2656 (YA); Ntale, bank and bed of Mbier River, 10 Dec 2010, F. Kuetegue 272, 273 (YA).

Habitat

Rocky or sandy riverbeds and by seasonal rivers, in wet evergreen and semi-deciduous rainforests to deserts.

Distribution

Benin, Cameroon (Fig. 7), Côte d’Ivoire, Nigeria, Somalia, South Africa, and Sudan.

Conservation status in Cameroon

Kanahia laniflora was not assessed by Onana and Cheek (2011). It is listed on http://www.redlist.org as Least Concern (LC) by Lansdown (2013). This is because the species, globally, is believed to be widespread and abundant throughout much of its known distribution area. The species is distributed from Saudi Arabia and Yemen, through Ethiopia and Somalia to Cote d’Ivoire and South Africa. The extent of occurrence of K. laniflora in Cameroon is about 78,700 km2; and area of occupancy of the species is about 32 km2. The taxon is currently known from 8 localities in the country. The localities where the species is found are proposed for timber exploitation and plantation development. Based on these threats and the progressive destruction of the vegetation in the localities, extent and/or quality of the habitats, the species is here assessed, as Vulnerable. IUCN Red List Category: Vulnerable VUB2ab (ii, iii).

Araceae

Anubias barteri Schott, Prodr. Syst. Aroid. 159 (1860)

Type

Equatorial Guinea, Fernando Po (Bioko), Barter 2045 (K).

Description

Hardy herb with thick creeping rhizome, prostrate; strongly rooted; green, lush, narrow shaped leaves 7–30 × 3–15 cm.

Specimens examined

Fenda, 60 km southeast of Kribi, 22 Jan 1962, R. Letouzey 4120 (YA); Nyon River, 49 km southwest of Eseka, 12 Mar 1965, A. J. M. Leeuwenberg 5136 (YA); road from Ebone to Yabassi at mile 10, 27 Dec 1967, P. Bamps 1636 (YA), Nguti-Kombon, bank of Kombon River, 5°13'N, 9°33'E, 13 Dec 2010, F. Kuetegue 239 (YA).

Habitat

Rocky beds of swift-flowing streams and rivers, or wet shrubby and bushy bank of rivers and streams; in rainforest.

Distribution

Cameroon (Fig. 8), Congo, Côte d’Ivoire, Gabon, Guinea, Liberia, and Nigeria.

Conservation status in Cameroon

Anubias barteri is listed on http://www.iucnredlist.org as Least Concern (LC) in central Africa in 2007 by Ghogue (2010a). The species was not assessed by Onana and Cheek (2011). The taxon is currently known from 16 localities. The extent of occurrence of A. barteri is about 7,600 km2 and has an area of occupancy of about 64 km2. The habitat is mainly threatened by urban development, road constructions and hydroelectric dams already built or at project stage. Despite the threats, and the fact that the habitats are under pressure, the species does not appear to qualify as threatened under the IUCN red list criterion (IUCN 2017). Though human pressure is expected to increase the loss of habitat and reduce area of occupancy and extent of occurrence (EOO), it is not expected that this will be significant. It is possible that the EOO was underestimated because only specimens with geographical coordinates were used to estimate the EOO. Based on these observations, A. barteri is assessed here as Near Threatened. IUCN Red List Category: Near Threatened (NT).

Cyperaceae

Cyperus rheophyticus Lye, Nordic J. Bot. 24 (3): 273 (2006)

Type

Cameroon, South West Division, Kupe-Muanenguba Division, Muambong, bank of Chide River, 3°58'N, 9°41'E, 02 Aug 1998, J.-M. Onana 585, (holotype: K; isotype: YA).

Description

Perennial herb, 30–50 cm high; deeply rooted; inflorescence terminal, with involucre bracts.

Specimens examined

Kodmin, beside a stream, 4°59'N, 9°42'E, 21 Nov 1998, M. Etuge 406 (YA).

Habitat

Forest streams and rivers, submerged during wet season.

Distribution

Cameroon (Fig. 9).

Conservation status in Cameroon

Cyperus rheophyticus is listed on http://www.iucnredlist.org as Vulnerable in 2017 (Cheek et al. 2017b). The taxon is currently known from five localities, and endemic to Cameroon. The extent of occurrence of this species is about 3,000 km2 and area of occupancy is about 20 km2. The localities where they occur are proposed for plantation development, timber exploitation and road construction. Not much has changed since the last assessment of Cheek et al. (2017b); here we maintain its status as Vulnerable. IUCN Red List Category: Vulnerable B1ab (iii) +2ab (iii).

Cyperus tonkinensis C.B.Clarke var. baikiei (C.B.Clarke ex Kük) S.S.Hooper, Kew Bull. 26 (3): 577 (1972)

Cyperus baikiei C.B.Clarke, Consp. Fl. Afr. [T.A. Durand & H. Schinz] 5: 550 (1894)

Cyperus kottensis Chem. Arch. Bot., Caen iv. Mem. No. 7, 23 (1931)

Type

Vietnam, Tonkin, Tu-Phap, 12 Apr 1888, Balansa 2831 (K).

Description

Herb, about 12 cm high, with hard tubers, connected by dark brown rhizome; stems dark brown and shiny; inflorescence spikelets, glumes brown.

Specimens examined

62 km southeast of Bafia, on Sanaga River, 4°75'N, 11°22'E, 27 Mar 1963, J. & A. Raynal 10538 (YA); Sanaga River, bridge near Nkong Njok, 4°10'N, 11°01'E, 12 Mar 1978, J. Lowe 3483 (YA); Bongossi Research Plot of the National Herbarium of Cameroon, bank of Sanaga River, 4°22'N, 11°16'E, 29 Mar 1987, L. Ake Asse 1859 (YA); near Nguti, Mbombe on Loa River, 29 May 2011, F. Kuetegue, 498 (YA).

Habitat

Sandy bars or beds of streams and rivers.

Distribution

Benin, Cameroon (Fig. 10), Central African Republic, Chad, Congo, Ghana, Guinea, Liberia, Mali, Nigeria, Senegal, and Sierra Leone.

Conservation status in Cameroon

Cyperus tonkinensis var. baikiei is not listed on http://www.iucnredlist.org nor assessed by Onana and Cheek (2011). The taxon is currently known from five localities. The extent of occurrence of this species is about 800 km2 and the area of occupancy is about 20 km2. Construction of a hydropower dam on the Sanaga River from which the species was collected is in progress. Based on this threat and the fact that the species is only currently known from five localities, C. tonkinensis var. baikiei is here assessed as Endangered. IUCN Red List Category: Endangered ENB1+2ab (ii, iii).

Cyperus cataractarum K.Schum ex. Engl., Veg. Erde 9(2): 200 (1908)

Pycreus cataractarum C.B.Clarke, Bot. Jahrb. Syst. 38(2): 132 (1906)

Type

Cameroon, Bipindi, 1899, G. Zenker 1935 (syntype: BR, K, P, P00573020, WAG).

Description

Tufted, grass-like leaves forming high sods (up to 30 cm thick cushions); roots forming large fibrous tussocks; stems smoothly glossy; leaves linear, green to dark green; spikelets greenish-white; glumes with a green midrib.

Specimens examined

27 km from Kribi in Kienké River, 2°52'N, 10°7'E, 27 Jan 1970, J. J. Bos 6168 (YA); Mpoume waterfalls on Nyong River at Makak, 3°28'N, 11°01'E, 01 Jan 1978, J. Lowe 3420 (YA); near Akonetyè village, Mboro waterfalls, 15 Jan 1978, A. Koufani 20 (YA).

Habitat

Banks, edges and beds of streams and rivers; in rainforest.

Distribution

Cameroon (Fig. 11), Congo, Gabon and Nigeria.

Conservation status in Cameroon

Cyperus cataractarum is not listed on http://www.iucnredlist.org nor assessed by Onana and Cheek (2011). The taxon is currently known from 6 localities. The extent of occurrence of this species is about 13,400 km2 and the area of occupancy is about 24 km2. The habitat of C. cataractarum is being progressively destroyed by plantation development and timber exploitation. Based on these threats, and extent and/or quality of habitat, the species is currently assessed as Vulnerable. IUCN Red List Category: Vulnerable VUB1+2ab (ii, iii).

Figures 11–19. 

11 Cyperus cataractarum K.Schum ex Engl. 12 Plectranthus cataractarum B.J.Pollard 13 Calvoa stenophylla Jacq.-Fél. 14 Eugenia dusenii Engl. 15 Biophytum talbotii (Baker f.) Hutch. & Dalziel 16 Biophytum zenkeri Guillaumin 17 Pandanus satabiei Huynh 18 Eragrostis barteri C.E.Hubb. 19 Ixora euosmia K.Schum.

Lamiaceae

Plectranthus cataractarum B.J.Pollard, Kew Bull 56(4): 976 (2001)

Type

Cameroon: Hunters path to Lake Njonji at side of seasonal watercourse, M. Cheek 5563 (holotype: K; isotypes: MA, MO, SCA, WAG, YA).

Description

Annual or perennial herb growing to 60 cm tall; stems decumbent to ascending, sub-woody at the base; leaves slightly fleshy, 20–45(-70) × 5–20(-25) mm, 2–2.5 times as long as broad; inflorescence terminal.

Specimens examined

Etinde, Njonji, footpath from Cameroon Development Corporation oil palm plantations to the summit, 24 Nov 1993, Williams 52 (K, SCA, WAG, YA); Bakossi Mts: Chutes de ‘Ile Ndip Medschang, 21 Nov 1998, Satabie 1109 (K, K000051130).

Habitat

Invariably growing in spray zone of waterfalls, on wet rocks or on river banks, up to flood level, of swift-running water; lowland or submontane evergreen forest, 300–1450 m alt.

Distribution

Cameroon (Fig. 12) and Equatorial Guinea.

Conservation status in Cameroon

Plectranthus cataractarum is listed on http://www.iucnredlist.org. The species was assessed as Vulnerable (Pollard and Paton 2003). Eight years later it was reassessed as Endangered (Onana and Cheek 2011). The taxon is currently known from three collecting localities. The extent of occurrence and the area of occupancy are both estimated to be less than 10 km2. The associated threats, such as forest logging and plantation establishment, mentioned by Pollard and Paton (2003) are still ongoing. Based on these threats, and that the habitats are still under pressure, the species is here re-evaluated as Endangered. IUCN Red List Category: Endangered ENB1+2ab (ii+iii).

Melastomataceae

Calvoa stenophylla Jacq.-Fél., Bull. Mus. Natl. Hist. Nat., B, Adansonia Sér. 4, 3(2): 143 (1981)

Type

Cameroon, 10 km Southeast of Zingui, 16 Mar 1968, R. Letouzey 9083. (Holotype: P; isotype: YA).

Description

Small herb, about 20 cm high; stem flexible; roots spreading and fibrous; leaves narrow-lanceolate 4–6 × 0.2–0.5 cm; flowers terminal, pink.

Specimen examined

Minsomo River, 10 km southeast of Zingui, 2°56'N, 9°54'E, 16 Mar 1968, R. Letouzey 9083 (YA).

Habitat

Rocks on bed of Minsomo River.

Distribution

Cameroon (Fig. 13) and Equatorial Guinea.

Conservation status in Cameroon

Calvoa stenophylla is listed on http://www.iucnredlist.org as Endangered (Cheek 2015). The species was assessed as Critically Endangered (Onana and Cheek 2011), since it was known from only one locality and the associated threats at the time. Cheek (2015) reassessed the species, globally as Endangered, since the number of localities has increased to two, and area of occupancy of 8 km2. The second locality is in Equatorial Guinea (Cheek 2015). In Cameroon, the species is only known from one locality and the area of occupancy is about 4 km2. The extent of occurrence (EOO) is estimated at 1 km2, following the IUCN preferred grid cell size for aquatic organisms (IUCN 2013, 2017). This was used by Cheek et al. (2015) in assessing the conservation status of Ledermanniella lunda Cheek (Podostemaceae) from Angola. The main threats are forest logging and agriculture activities. Based on these threats, and the continuous decline of vegetation in the area, extent and /or quality of habitat C. stenophylla is here assessed, as Critically Endangered. IUCN Red List Category: Critically Endangered CRB2ab (ii, iii).

Myrtaceae

Eugenia dusenii Engl., Notizbl. Königl. Bot. Gart. Berlin 2: 289 (1899)

Myrtus dusenii Kuntze, Deutsche Bot. Monatsschr. 21: 173 (1903)

Type

Cameroon. Mundemba, Mana bridge, 4°58'N, 7°00'E, 11 Jan 1998, M. Cheek 8845 (holotype: K; isotype: YA).

Description

Small erect shrub, up to 1.5 m; stem very flexible; leaves small and narrow, 2–5 × 0.3–0.5 cm; strongly rooted; white-flowered.

Specimens examined

Ndian waterfalls at Bulu docks, 4°56'N, 8°51'E, 17 Jan 1985, D. W. Thomas 1985 (YA); Ndian River, west of Mundemba, 5°02'N, 8°53'E, 21 Jan 1986, J. Nemba & D. W. Thomas 319 (YA); Mundemba, Mana bridge, 4°58'N, 7°00'E, 11 Jan 1998, M. Cheek 8845 (YA).

Habitat

Beds of swift-running rivers; seasonally inundated river banks; rocks at waterfalls, in evergreen rainforest.

Distribution

Cameroon (Fig. 14), endemic to Cameroon.

Conservation status in Cameroon

Eugenia dusenii is not listed on http://www.iucnredlist.org, but it was assessed as Vulnerable VU in Onana and Cheek (2011). The taxon is endemic to Cameroon and currently known from four localities. The area of occupancy is estimated to be about 16 km2, and the extent of occurrence is estimated at 4 km2. Plantation development and illegal logging of timber are ongoing at the localities. Based on these threats, and the continuous decline of vegetation cover in the area, and extent and /or quality of habitat E. dusenii is currently reassessed as Endangered. IUCN Red List Category: Endangered ENB2ab (ii, iii).

Oxalidaceae

Biophytum talbotii (Baker f.) Hutch. & Dalziel, Fl. W. Trop. Afr. 1: 140 (1927)

Biophytum kamerunense Engl. & R.Kunth ex Engl., Veg. Erde 9(3,1): 717 (1915)

Oxalis talbotii Baker f., Cat. Pl. Oban 16 (1913)

Type

Liberia, 02 Nov 1910, Bunting, R. H. 103 (holotype: BM).

Description

Perennial herb, woody stem, up to 30 cm high; roots spreading; leaves in shape of umbrella; flowers pink.

Specimens examined

Njabilobé, 54 km southeast of Kribi, 12 Mar 1963, J. & A. Raynal 10425 (YA); Kienke River, Kribi, 2°56'N, 9°55'E, 20 Jun 1969, J. J. Boss 4900 (YA); near Numba, 45 km northeast of Mamfe, 5°50'N, 9°42'E, 18 Aug 1975, R. Letouzey 14331 (YA); Mamfe road, near Numba, 16 Dec 2012, F. Kuetegue 400 (YA) .

Habitat

Riverbeds and earthbanks of shaded forest streams, periodically inundated rocks in rivers; in rainforest.

Distribution

Cameroon (Fig. 15), Liberia and Nigeria.

Conservation status in Cameroon

Biophytum talbotii is not listed on http://www.iucnredlist.org nor assessed by Onana and Cheek (2011). The taxon is currently known from 13 localities. Extent of occurrence of this species is about 38,000 km2 and the area of occupancy is about 56 km2. Forest logging is the main threat at these habitats. Based on this threat and the continuous decline of vegetation cover in the area, extent and /or quality of habitat B. talbotii is here assessed as Vulnerable. IUCN Red List Category: Vulnerable VU B2ab (ii, iii).

Biophytum zenkeri Guillaumin, Notul. Syst. (Paris) 1: 26 (1909)

Type

Cameroon, 01 Jan 1908, G. Zenker 3428 (BM, BR, G; HBG, K, K000419376, M, P, W).

Description

Perennial herb, up to 30 cm tall, forming dense clumps; leaves in rosette or nearly so; flowers yellow.

Specimens examined

Cross River ferry between Ikom and Manfe, 07 Apr 1955, J. K. Morton K318 (YA); Korup, rocky river bank of Mana River, 4°55'N, 8°50'E, 08 Jun 1983, D. W. Thomas 2164 (YA); Ndian Division Mundemba, in Mana River, 5°00'N, 8°50’E, 21 Nov 1986, Stephen D. Manning 896 (YA).

Habitat

In rock crevices in riverbeds, seasonally flooded; in forest.

Distribution

Angola, Cameroon (Fig. 16), Congo, Gabon and Nigeria.

Conservation status in Cameroon

Like the species before it, Biophytum zenkeri is not listed on http://www.iucnredlist.org. The taxon is currently known from 9 localities. The extent of occurrence of this species is about 80,000 km2 and its area of occupancy is about 36 km2. Plantation development is in progress at two of the localities and this may affect the survival of the species. Based on this threat, and the continuous decline of vegetation cover in the area, extent and /or quality of habitat B. zenkeri is here assessed as Vulnerable. IUCN Red List Category: Vulnerable VU B2ab (ii, iii).

Pandanaceae

Pandanus satabiei Huynh, Bull. Mus. Natl. Hist. Nat., B, Adansonia Sér. 4, 6(3): 347 (1984)

Type

Cameroon, near the Ndonga River (30 km W Edea), 20 Dec 1973, R. Letouzey 12472 (holotype: P; isotype: YA).

Description

Shrub or small tree of about 5 m tall; strongly rooted; leaves narrow 60–80 × 2–4 cm, spine on the borders; fruit green.

Specimens examined

Wouri River, near Bekoko, Douala-Nkongsamba road, 16 Jun 1983, Satabie 674 (YA); bed of Dilolo River at Bolomeboka, Nkonyé, 4°51'N, 9°28'E, 22 Mar 2011, F. Kuetegue 462 (YA); Mongo River at Mbakwa Super, Nkonyè, 5°01'N, 9°25'E, 24 Mar 2011, F. Kuetegue 463 (YA).

Habitat

Banks of rivers subject to flooding.

Distribution

Cameroon (Fig. 17).

Conservation status in Cameroon

Pandanus satabiei was not assessed by Onana and Cheek (2011) nor listed on http://www.iucnredlist.org. The taxon is endemic to Cameroon and currently known from five localities. The extent of occurrence of this species is about 2,900 km2 and the area of occupancy is about 20 km2. Human settlements are developing around one collecting locality; also arable farming is in progress along the rivers. Based on these threats, and the continuous decline of vegetation cover in the area, extentand /or quality of habitat, P. satabiei is here assessed as Endangered. IUCN Red List Category: Endangered EN B1+2ab (ii, iii).

Poaceae

Eragrostis barteri C.E.Hubb., Fl. W. Trop. Afr. 2: 514 (1936)

Eragrostis fluviatilis A.Chev., Bull. Mus. Nalt. Hist. Nat. sér 2, 20: 472 (1948)

Type

Nigeria, 1858, C. Barter 877 (syntype: K, K000366508; isotype: P).

Description

Perennial grass, robust, of about 1 m high; leaves lanceolate; inflorescence in open panicle.

Specimens examined

Nkokmen II, at 8 km east of Yingui, at the bank of Makombe River, 4°32'N, 10°15'E, 09 Jan 1972, D. van der Zon 10939 (YA). Mpoumé falls on Nyong River, 9 km south of Makak 3°28'N, 11°00'E, 20 Jan 1977, J. Lowe 3188 (YA); Sanaga River at Nkongnjok, 4°10'N, 11°01'E, 12 Jan 1978, J. Lowe 3471 (YA); Kikot (Douala-Bafia road), near bridge, bank of Sanaga, 3°51'N, 11°30'E, 16 Dec 2012, F. Kuetegue 535 (YA).

Habitat

Among rocks, and sandbanks on riverbed or streams.

Distribution

Cameroon (Fig. 18), Congo, Côte d’Ivoire, Ghana, Mali, Nigeria, Senegal and Sierra Leone.

Conservation status in Cameroon

Eragrostis barteri was not assessed by Onana and Cheek (2011), nor listed on http://www.iucnredlist.org. The taxon is currently known from 10 localities some of which are on the Sanaga River. The extent of occurrence of the species is about 260,000 km2 and area of occupancy is about 44 km2. The proposed dam on Sanaga River will destroy some habitats of the species. Based on this threat, and the continuous decline of vegetation cover in the area, extent and /or quality of habitat, E. barteri is currently assessed as Vulnerable. IUCN Red List Category: Vulnerable VU B2ab (ii, iii).

Rubiaceae

Ixora euosmia K.Schum., Bot. Jahrb. Syst. 33(2): 355 (1903)

Ixora degemensis Hutch. & Dalziel, Fl. W. Trop. Afr. 2: 86 (1931)

Type

Cameroon. Bipindi, bank of Lokoundje River, 02 Oct 1896, G. Zenker 1108, (holotype: K; isotypes: BR, HBG, MO, WAG, Z).

Description

Shrub or small tree up to 5 m tall; leaves narrowly elliptic-oblong 10–19 × 2–4.5 cm; inflorescence terminal.

Specimens examined

Lobe River, 7 km south of Kribi, 2°53'N, 9°54'E, 20 Feb 1969, J. J. Bos 3940 (YA); Songloulou falls, at 25 km southwest of Ngambé, Massock-Songloulou road, 3°35'N, 9°44'E, 24 Jan 1972, R. Letouzey 11103 (YA); 5 km southeast of Bipindi, 3°04'N, 10°25'E, 14 Jan 1987, Stephen D. Manning 1343 (YA); Nguti-Ntalè, Mbièr River, 5°15'N, 9°34'E, 13 Dec 2010, F. Kuetegue 226 (YA).

Habitat

Inundated sandy or rocky banks of rivers, between rocks in streams or rivers, waterfalls; riverine forest.

Distribution

Cameroon (Fig. 19), Equatorial Guinea and Nigeria.

Conservation status in Cameroon

Ixora euosmia was not assessed by Onana and Cheek (2011) nor listed on http://www.iucnredlist.org. The taxon is currently known from 10 localities. The extent of occurrence of this species is about 36,900 km2 and the area of occupancy is about 44 km2. There is a dam built (hydro-electric dam at Songloulou on Sanaga River), and a proposed project, Memve’ele hydro-electric dam at Nyabezan (Ntem waterfall); and mining projects envisaged in Kribi. Based on these threats and the continuous decline of vegetation cover in the area, extent and /or quality of habitat I. euosmia is here assessed as Endangered. IUCN Red List Category: Endangered ENB2ab (ii, iii).

Ixora inundata Hiern, Fl. Trop. Afr. 3: 166 (1877)

Type

Gabon. Cristal Mountains, 1862, Mann 1731 (holotype: K; isotype: P).

Description

Shrub up to 1.5 m tall; strongly rooted; stems tough; leaves lanceolate 4–11 × 1–2.5 cm; flowers translucent white.

Specimens examined

Near Nkolemvom, 20 km southeast of d’Ebolowa, 2°54'N, 11°09'E, 03 Mar 1970, R. Letouzey 9986 (YA); between Bulu and Ekum Bako, SW Region, 4°56'N, 8°52'E, 01 Jun 1984, D. W. Thomas 3499 (YA); at the bank of Cross River, north of Nsanaragati, 5°52'N, 8°54'E, 16 Dec 1986, Stephen D. Manning 1217 (YA).

Habitat

Rocky bank of rivers, periodically inundated; between rocks in rivers.

Distribution

Cameroon (Fig. 20) and Gabon.

Conservation status in Cameroon

Ixora inundata is not listed on http://www.iucnredlist.org. However, in Onana and Cheek (2011), the species was assessed as Endangered. The taxon is currently known from five localities. The extent of occurrence of the species is about 56,000 km2, and the area of occupancy is about 20 km2. The proposed dam on Ntem River is very likely to threaten the survival of I. inundata. Based on this threat and the continuous decline of vegetation cover in the area, extent and /or quality of habitat the species is assessed here as Endangered. IUCN Red List Category: Endangered ENB2ab (ii, iii).

Figures 20–25. 

20 Ixora inundata Hiern 21 Virectaria angustifolia (Hiern) Bremek 22 Virectaria salicoides (C.H.Wright) Bremek 23 Deinbollia angustifolia D.W.Thomas 24 Deinbollia saligna Keay 25 Podostemaceae distribution.

Virectaria angustifolia (Hiern) Bremek., Verh. Kon. Ned. Akad. Wetensch, Afd. Natuurk., Sect. 2. 48(2): 21 (1952)

Virecta angustifolia Hiern, Fl. Trop. Afr. 3: 48 (1877)

Virecta heteromera K.Schum., Bot. Jahrb. Syst. 23(3): 422 (1896)

Virectaria heteromera (K.Schum.) Bremek., Verh. Kon. Ned. Akad. Wetensch., Afd. Natauurk., Sect. 2, 48(2): 21 (1952).

Type

Gabon, Mounts of Cristal, July 1862, G. Mann 1686 (holotype: K).

Description

Erect herb, up to 30 cm tall; leaves linear to oblanceolate 5–15 × 1–2 mm; flowers white.

Specimens examined

50 km southeast of Kribi, 2°42'N, 10°12'E, 14 Mar 1968, R. Letouzey 9011 (YA); bank of Mana River at Ndian, 4°58'N, 8°51'E, 09 Dec 1983, D. W. Thomas 50588 (YA); Ndian River northwest of Mundemba, 00 Oct 1986, Stephen D. Manning 894 (YA); Ntale, bank and bed of Mbier and Essembe River, 23 Dec 2010, F. Kuetegue 319 (YA).

Habitat

Rocks of riverbeds and inundated banks, up to flood level of streams and rivers, submerged during rainy season.

Distribution

Cameroon (Fig. 21), Gabon, Ghana and Nigeria.

Conservation status in Cameroon

Virectaria angustifolia is not listed on http://www.iucnredlist.org, nor assessed by Onana and Cheek (2011). The taxon is currently known from more than 7 localities. The extent of occurrence of the species is about 66,500 km2, and its area of occupancy is about 28 km2. Timber exploitation and plantation development are in progress at the collecting localities. Based on these threats and the continuous decline of vegetation cover in the area, extent and /or quality of habitat V. angustifolia is here assessed as Vulnerable. IUCN Red List Category: Vulnerable VB1+2ab (ii, iii).

Virectaria salicoides (C.H.Wright) Bremek., Verh. Kon. Ned. Akad. Wetensch., Afd. Natuurk., Sect. 2, 48(2): 21 (1952)

Virecta salicoïdes C.H.Wright, Bull. Misc. Inform. Kew 1898(1430): 302 (1898)

Type

Cameroon, Mfoa, rocky bank of Mbei River, 00 Oct 1827, G. L. Bates 527 (holotype: K; isotypes: BM, P).

Description

Herb 25 cm high; stems flexible and tough; strongly rooted; leaves narrow 3–9 × 0.5–0.9 cm; inflorescence terminal.

Specimen examined

Nkolebenga, northwest of d’Ebianemeyong, near Nyabesan, 60 km east of Campo, 2°25'N, 10°20'E, 11 Apr 1970. R. Letouzey 10357 (YA).

Habitat

Rocks at banks and beds of rivers and streams.

Distribution

Cameroon (Fig. 22) and Gabon.

Conservation status in Cameroon

Virectaria salicoides is not listed on http://www.iucnredlist.org, nor assessed by Onana and Cheek (2011). The taxon is currently known from two localities (Kribi and Ebianemeyong). The extent of occurrence of the species is estimated at less than 100 km2, and its area of occupancy is about 4 km2. The habitat is threatened by dam construction (Memve’ele Hydro-electric dam on Ntem waterfall at Nyabesan). Based on this threat, and the continuous decline of vegetation cover in the area, extent and /or quality of habitat V. salicoides is here assessed as Endangered. IUCN Red List Category: Endangered EN B2ab (ii, iii).

Sapindaceae

Deinbollia angustifolia D.W.Thomas, Ann. Missouri Bot. Gard. 73(1): 219 (1986)

Type

Cameroon – SouthWest Region, near Mundemba, 4°56'N, 8°52'E, rocky bank of Idu River at Bulu on path to Ekumbako, 10 m, 07 Mar 1984, D. W. Thomas 3253 (holotype: MO; isotypes: K, P, YA).

Description

Stenophyllous shrub of about 1 m high; roots spreading and deep; stems strong but flexible; leaves narrow 20–25 × 1–1.5 cm, grouped at the summit of the stem.

Specimens examined

Korup Reserve, 4°55'N, 8°50'E, 16 Jul 1983, D. W. Thomas 2243 (YA); between Bulu and Dibunda, 4°55'N, 8°52'E, 07 Mar 1984, D. W. Thomas 3253 (YA); between Bulu and Ekumbako, 4°56'N, 8°52'E, 00 Jun 1984, D. W. Thomas 3497 (YA).

Habitat

Rocky bed of rivers, on banks of streams and rivers.

Distribution

Cameroon (Fig. 23).

Conservation status in Cameroon

Deinbollia angustifolia is listed on http://www.iucnredlist.org as Vulnerable by Cheek (2017a). It was earlier assessed in Onana and Cheek (2011) as Vulnerable. The taxon is endemic to Cameroon and currently known from three localities. The extent of occurrence of this species is estimated less than 100 km2, and the area of occupancy is about 12 km2. The habitat of D. angustifolia is threatened by illegal timber logging. Based on this threat, and the continuous decline of vegetation cover in the area, extent and /or quality of habitat, the assessment of Cheek (2017a) is maintained as Vulnerable. IUCN Red List Category: Vulnerable VU B2a b (ii, iii).

Deinbollia saligna Keay, Bull. Jard. Bot. État Bruxelles 26: 193 (1956)

Type

Cameroon, Ndian, Kumba, 03 Mar 1936, Smith Cam 80/36 (holotype: K, K000093228; isotype: FHI).

Description

Shrub or small tree up to 2.5 m tall; sparingly to much branched; branches thick; stems strong and flexible; leaves clustered terminally; lanceolate 6–10 × 0.5–1 cm; flowers white.

Specimens examined

Canyon of Ntem, 20 km southwest of Nyabessan, 01 Dec 1982, B. A. Nkongmeneck 410 (YA); Mana River at Korup, 4°55'N, 8°50'E, 00 Dec 1983, D. W. Thomas 2205 (YA); Ndian, on Ndian (Mana) waterfall, 4°56'N, 8°51'E, 17 Jan 1985, D. W. Thomas 4268 (YA).

Habitat

Inundated rocky bed and bank of rivers or streams.

Distribution

Cameroon (Fig. 24), Ghana and Nigeria.

Conservation status in Cameroon

Deinbollia saligna is listed on www.iucnredlist.org. It was assessed globally as Vulnerable (World Conservation Monitoring Centre, 1998). In Onana and Cheek (2011) the species was assessed for the Red data Checklist of Cameroon as Vulnerable. This taxon is currently known from four localities. The extent of occurrence of the species is estimated at less than 100 km2, and the area of occupancy is about 16 km2. The localities are threatened by proposals for dam construction and timber extraction. Based on these threats, and the continuous decline of vegetation cover in the area, extent and /or quality of habitat D. saligna is here reassessed as Endangered: IUCN Red List Category: Endangered ENB2ab (ii, iii).

Family in which all species are rheophytic (Podostemaceae)

The present study and herbarium data have shown that 43 species in 12 genera in the Podostemaceae (riverweed) family have so far been documented from the study area. The results revealed six monotypic genera: Leiothylax, Letestuella, Stonesia, Tristicha, Winklerella, and Zehnderia. The genus Inversodicraea has 10 species, Saxicolella has four while three genera Dicraeanthus, Djinga, and Macropodiella have two; and the largest genus in our area Ledermanniella has 17 species. In an earlier work Ameka et al. (2002) recognized 53 rheophytic species including 33 Podostemaceae for Cameroon. Since then 13 species have been added, 10 of which are in the Podostemaceae family. The Podostemaceae added within the last few years are the result of a deliberate search for the riverweed family in Cameroon. If similar efforts are made to collect the rheophytes in other African countries, many more species would be described for the continent. Apart from the Podostemaceae, the Hydrostachyaceae is the only other family in which all species are rheophytic in Africa (Ameka et al. 2002). So far the Hydrostachyaceae has not been recorded in the study area. Species of the two families are important since they are indicators of river health and also are the dominant macrophytes in tropical river systems; contributing to primary production and oxygenation of the river water (Quiroz et al. 1997, Ameka 2000). The Podostemaceae, for example, serve as substrate for epiphytic algae e.g., diatoms and cyanobacteria (blue-green algae) and other microscopic organisms (Ameka 2000). They also are habitats for invertebrate larvae (e.g., larvae of Simulium (black) fly, and nymphs of dragonfly and mayfly) that seek shelter and feed (Quiroz et al. 1997, Ameka per. obs.).

Podostemaceae

Description. Podostemaceae are annuals or perennials, that grow attached to rocks, in fast-flowing water, by rhizoids, or expanded holdfast; resembling algae or mosses. They produce flowers and fruits during the dry season when the water level in the rivers or streams drops.

Dicraeanthus africanus Engl., Bot. Jahrb. Syst. 38(1): 96 (1905)

Dicraeanthus ramosus H.E.Hess, Ber. Geobot. Inst. Eidg. Techn. Hochsch. Rübel Heft 32: 187 (1961).

Type

Cameroon, Winkler 901 (holotype: B).

Specimens examined

Edea at Sanaga waterfall, Annet 498 (P); 8 km S Kribi Lobe fall, J.J. Bos 3590, 3887, 3888 (K, WAG); Ngaoundere, Vina waterfall, Dulieu 4 (P); Natchigal, 62 km southeast of Bafia, J. & A. Raynal 10544 (P).

Habitat

River rapids and waterfalls.

Distribution

Cameroon (Fig. 25), Gabon.

Conservation status in Cameroon

Dicraeanthus africanus has been assessed for the IUCN Red List, globally, in 2007 as Least Concern (Ghogue 2010b). This species was not assessed by Onana and Cheek (2011). Two localities, waterfalls, are known for this species. The extent of occurrence and the area of occupancy are both estimated at less than 10 km2. There are currently two major threats to the survival of this species at the Edea and Lobe waterfalls. First is the planned hydropower dam on the Sanaga River. Secondly the waterfalls on Lobe River is a big tourist attraction site. The dam across the river and activities (e.g., trampling) of tourists will adversely impact the habitats of the species and affect its survival. D. africanus is currently reassessed as Critically Endangered. IUCN Red List Category: Critically Endangered CRB1+2ab (iii).

Dicraeanthus zehnderi H.E.Hess, Ber. Geobot. Inst. Eidg. Techn. Hochsch. Stiftung Rŭbel Heft 32: 188 (1961)

Type

Cameroon, Edea, 30 Jan 1951, Zehnder 259 (syntype: Z, ZT).

Specimens examined

Edea at Sanaga waterfall, Zehnder 259, 260, 262 (ZT); Sanaga waterfalls, 30 Jan 1951, Hess 51/270 (ZT).

Habitat

Growing in river rapids and waterfalls of Sanaga.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Dicraeanthus zehnderi was listed on http://www.iucnredlist.org as Critically Endangered (Ghogue 2010c). It was also assessed by Onana and Cheek (2011) as Critically Endangered since it has not been collected for many decades. The only known collecting locality for D. zehnderi is the waterfall on Sanaga River at Edea. The extent of occurrence and the area of occupancy are both estimated at 4 km2. The hydropower dam on the waterfall will adversely affect the survival of this species and other Podostemaceae species present at this locality. The taxon is here reassessed as Critically Endangered. IUCN Red List Category: Critically Endangered CRB1+2ab (iii).

Djinga cheekii Ghogue, Huber & Rutish., Nordic J. Bot. 31(4): 458 (2013)

Type

Cameroon, near Manjo, 12 Jan 2011, J. P. Ghogue 2125 (YA, Z, ZT).

Specimens examined

Littoral Province, Mantem River, near Manjo, on the Douala – Nkongsamba highway, 4°49'N, 9°46'E, 12 Jan 2011, J.-P. Ghogue 2126 and 2128 (K, YA, Z, ZT); Mbo River, Manjo (Manengole Village), 4°52'N, 9°51'E, 12 Dec 2004, R. Imaichi, Y. Kita and J.-P. Ghogue CMR35 (TNS, Z, ZT).

Habitat

River rapids.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Djinga cheekii is not listed on the http://www.iucnredlist.org. The taxon is known only from the type locality, Mantem River near Manjo. The extent of occurrence is estimated as 4 km2, and area of occupancy is about 4 km2. The main threat at the locality is agriculture. Based on this threat, and the continuous decline of vegetation cover in the area, extent and /or quality of habitat the taxon is here assessed as Critically Endangered. IUCN Red List Category: Critically Endangered CRB1+2ab (iii).

Djinga felicis C.Cusset, l. Cameroun 30: 58 (1987)

Type

Cameroon, Adamawa, north of mount Djinga, 29 Oct 1967, H. Jacques – Felix. 8889 (holotype: P).

Specimen examined

Adamawa stream, north of mount Djinga, 29 Oct 1967, Jacque-Félix 8889 (holo-P).

Habitat

Mt. Djinga, Adamaoua, near Tignere, river rapids.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

This taxon, D. felicis, has not yet been assessed for the IUCN Red List. This species was assessed by Onana and Cheek (2011) as Critically Endangered since known from a single collection at the time. The species is most likely extinct at the type locality, Djinga Mts, Admmoua, north-western Cameroon. There are two other localities for the species, Juafef waterfall, where a hotel has been built, which is visited by many tourists coming into that area of Cameroon; and the other Anyajua waterfall is in an agricultural landscape, all in NW Cameroon (Ghogue et al. 2009). The extent of occurrence and area of occupancy are both estimated at 4 km2 each. Tourism and agricultural activities will adversely affect the habitat of the species. D. felicis is, therefore, reassessed currently as Critically Endangered. IUCN Red List Category: Critically Endangered CRB1+2ab (iii).

Inversodicraea achoundongii J.J.Schenk, R.Herschlag & D.W.Thomas, Syst. Bot. 40(2): 542 (2015)

Type

Cameroon, West of Nyabezan, 01 Dec 1992, D.W. Thomas & G. Achoundong 9642 (YA).

Specimen examined

Ntem River, west of Nyabessan, 02°24'N, 10°22'E, 01 Dec 1992, D. W. Thomas & G. Achoundong 9642 (YA).

Habitat

Memve’ele waterfalls, Ntem River, alt. 395 m.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Inversodicraea achoundongii is yet to be assessed for the IUCN Red List. The taxon is currently known only from the type locality at Memve’ele waterfalls on the Ntem River. The extent of occurrence and area of occupancy are both estimated at 4 km2 each. The proposed hydropower dam on the Ntem River will certainly impact the survival of the species. Based on this threat, the species is here assessed as Critically Endangered. IUCN Red List Category: Critically Endangered CRB1+2ab (iii).

Inversodicraea bosii (C.Cusset) Rutish. & Thiv, Plant Syst. Evol. 283: 57 (2009)

Ledermanniella bosii C.Cusset, Bull. Mus. Natl. Hist. Nat., B, Adansonia 4: 385 (1984)

Type

Cameroon, South of Kribi, 08 Jan 1969, J.J. Bos 3592 (YA). Basionym: Ledermanniella bosii C.Cusset, Bull. Mus. Natl. Hist. Nat., B, Adansonia 4: 385 (1984).

Specimens examined

South of Kribi on Lobe waterfall, 08 Jan 1969, J.J. Boss 3592 (K, WAG, P); near Bongola, Ntem waterfall, Dec, R. Letouzey 15333 (P); South Region, south Kribi, Lobe waterfall, 08 Jan 1969, J.J. Boss 3597 (WAG).

Habitat

Lobe waterfall, south of Kribi.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Inversodicraea bosii is listed on http://www.iucnredlist.org. The taxon was assessed as Endangered (Ghogue 2017a). Onana and Cheek (2011) assessed this species earlier as Endangered. The species is known from two localities, Campo waterfalls and Lobe waterfalls at Kribi. The extent of occurrence and area of occupancy are both estimated at 4 km2 each. Based on the continuing decline in quality of the habitat of the species at Lobe waterfalls due to activities of tourists; and the possible adverse effect of the proposed hydropower dam near Campo waterfalls the assessment of Onana and Cheek (2011) and Ghogue (2017a) cannot be maintained. The species is here reassessed as Critically Endangered. IUCN Red List Category: Critically Endangered CRBI+ B2ab (iii).

Inversodicraea cristata Engl., Veg. Erde 9(3, 1): 274 (1915)

Ledermanniella cristata (Engl.) C.Cusset, Adansonia sér. 2, 14(2): 273 (1974)

Type

Cameroon, near Malaka, Nov, Ledermann 1173 (lectotype: B).

Specimens examined

Near Malaka, 500 m alt., Nov, Ledermann 1173, 1189 (U); Mari River waterfall, c. 8 km north of Betare Oya, 05 Feb 1966, Leeuwenberg 7761 (WAG, YA); in Mvigili, northwest of Moan, 24 km southeast of Nyabezan, Mar, J. & A. Raynal 10263 (P); Maan (24 km southeast of Nyabezan), rocky bank of Mvigili River, northwest of the village, 06 Mar 1963, J. & A. Raynal 10263 (P, YA).

Habitat

River rapids.

Distribution

Angola, Cameroon (Fig. 25), Central African Republic, Equatorial Guinea, Gabon.

Conservation status in Cameroon

Inversodicraea cristata is listed on http://www.iucnredlist.org. The taxon was assessed globally as Vulnerable (Ghogue 2017b). The species is known from five localities. The extent of occurrence of I. critata is about 73,144 km2 and the area of occupancy is about 24 km2. The main threats currently known from the localities are mining and agriculture. Based on these threats, and the continuous decline of vegetation cover in the area, extent and /or quality of habitat, I. cristata is currently assessed as Vulnerable IUCN Red List Category: Vulnerable VUB1+2ab (iii).

Inversodicraea ebo Cheek, Blumea 62: 125 (2017)

Type

Cameroon, Yabassi, near Locndeng, 07 Dec 2013, van der Burgt 1716 (YA).

Specimens examined

Cameroon, Littoral Region, Yabassi, near Locndeng, Ebo River, 07 Dec 2013, van der Burgt 1716 (YA).

Habitat

On rocks in river rapids.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Inversodicraea ebo is not listed on http://www.iucnredlist.org. The taxon is known only from the type locality. The extent of occurrence and the area of occupancy are both estimated at about 4 km2 each. The main threats at the locality are forest logging, mining and agriculture. The species is here assessed as Critically Endangered. IUCN Red List Category: Critically Endangered CRB1+2ab (iii).

Inversodicraea eladii Cheek, Blumea 62: 151 (2017)

Type

Cameroon, Campo Ma`an area, 30 Nov 2001, M. Elad & P. Tchouto 1485A (YA).

Specimen examined

Cameroon, South Region, Campo Ma’an area, Lobe, Lobe waterfalls, 30 Nov 2001, M. Elad & P. Tchouto 1485A (YA).

Habitat

On rocks in waterfall near the sea, in evergreen forest zone.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Inversodicraea eladii as for the species before it is not as yet assessed for the IUCN Red List. The taxon is known from one locality. The extent of occurrence and the area of occupancy are both estimated at 4 km2 each. The main threat at the locality is touristic activity. The species is here assessed as Critically Endangered. IUCN Red List Category: Critically Endangered CRB1+2ab (iii).

Inversodicraea kamerunensis Engl., Veg. Erde 9(3, 1): 274 (1915)

Ledermanniella kamerunensis (Engl.) C.Cusset, Adansonia sér. 2, 14(2): 274 (1974).

Type

Cameroon, Campo, near Dipikar, Aug, Ledermann 440a (YA).

Specimen examined

Campo River waterfalls, near Dipikar, 00 Aug 1908, Ledermann 440a (YA).

Habitat

Waterfalls in low altitudes.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Inversodicraea kamerunensis is listed on http://www.iucnredlist.org as Vulnerable (Ghogue 2017c). It was assessed by Onana and Cheek (2011) as Critically Endangered. The species is endemic to Cameroon and known from only the type locality; the species has not been collected since 1908. The extent of occurrence and the area of occupancy are both estimated at 4 km2 each. The main threat at this locality is dam construction on Ntem River. I. kamerunensis is here reassessed and Critically Endangered status maintained. IUCN Red List Category: Critically Endangered CRB1+2ab (ii, iii).

Inversodicraea ledermannii Engl., Veg. Erde 9(3, 1): 274 (1915)

Ledermanniella ledermannii (Engl.) C.Cusset, Adansonia sér. 2, 14(2): 274 1974)

Type

Cameroon, South Region, near Kribi, Grand Batanga, Ledermann 225 (YA).

Specimens examined

SW Region, Korup National Park, 5°01'N, 8°50'E, 50 m, 5–15 Dec 1984, D.W. Thomas 4135A (K, P); near Kribi, Lobe waterfalls, Grand Batanga, Ledermann 225 (U); 6 km from Kribi, Lobe waterfalls, De Wilde 2875 (P, YA).

Habitat

River rapids.

Distribution

Angola, Cameroon (Fig. 25), Côte d’Ivoire, Gabon, Guinea, Sierra Leone.

Conservation status in Cameroon

Inversodicraea ledermannii is listed on http://www.iucnredlist.org as Least Concern, globally (Diop 2017). The taxon is known from five localities. The extent of occurrence of I. ledermannii is about 29,454 km2 and the area of occupancy is about 20 km2. The main threats currently known from the localities are logging, agriculture and touristic activities. Based on these threats, and the continuous decline of vegetation cover in the area, extent and/or quality of habitat, I. ledermannii is currently reassessed as Vulnerable. IUCN Red List Category: Vulnerable VUB2ab (iii).

Inversodicraea ntemensis (Y.Kita, Koi, Rutish. & M.Kato) J.J.Schenk, R.Herschlag & D.W.Thomas, Syst. Bot. 40(2): 542. (2015)

Ledermanniella ntemensis Y.Kita, Koi, Rutish. & M.Kato; Acta Phytotax. Geobot. 59: 224 (2008)

Type

Cameroon, R. Imaichi Kita, Y. & J. P. Ghogue CMR 65 (YA). Basionym: Ledermanniella ntemensis Y.Kita, Koi, Rutish. & M.Kato; Acta Phytotax. Geobot. 59: 224 (2008).

Specimens examined

South Region, Canon of Ntem, 30 km southwest of Nyabessan, 01 Dec 1982, Nkongmeneck 420 (YA); Ntem waterfalls, near Bongola, 40 km southeast of Campo, 10 Dec 1979, R. Letouzey 15333 (P, YA); Campo a’an area, Memve’ele waterfalls, 2°24'N, 10°21'E, 17 Jan 2002, P. Tchouto 3373 (K, KRI, SCA, WAG, YA).

Habitat

Rapids of Ntem River.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Inversodicraea ntemensis is not listed on http://www.iucnredlist.org. It was assessed in Onana and Cheek (2011) as Critically Endangered. The taxon is endemic to Cameroon and to the Ntem River. The extent of occurrence is about 4 km2, and the area of occupancy is about 4 km2. The main threat to the survival of the species is dam construction on Ntem River. The species is here reassessed and maintained as Critically Endangered. IUCN Red List Category: Critically Endangered CRB1+2ab (ii, iii).

Inversodicraea tchoutoi Cheek, Blumea 62: 149 (2017)

Type

Cameroon, P. Tchouto 3378 (YA).

Specimens examined

South Region, Campo Ma’an Area, Boucle du Ntem, near Meyas Ntem, 2°20'N, 10°35'E, 480 m alt., 16 Feb 2001, P. Tchouto 3170 (K, KRI, SCA, WAG); Memve’ele waterfalls, 2°24'N, 10°21'E, 360 m alt., 17 Jan 2002, P. Tchouto 3376 (K, KRI, SCA, R. Letouzey 10299 (P).

Habitat

Waterfalls in evergreen forest.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Inversodicraea tchoutoi has not yet been assessed for the IUCN Red List. The taxon is known from only the Memve’ele waterfalls. The extent of occurrence is about 2 km2, and the area of occupancy is also about 2 km2. The main threat is the construction of a dam on the Ntem River and touristic activities. The species is here assessed as Critically Endangered. IUCN Red List Category: Critically Endangered CRB1+2ab (ii, iii).

Inversodicraea xanderi Cheek, Blumea 62: 147(2017)

Type

Cameroon, Campo, 04 May 2016, van der Burgt 1940 (holotype: K; isotypes: P, Z).

Specimens examined

South Region, Campo, Campo-Ma’an National Park, north of the road Campo to Ma’an, 2°20'N, 10°13'E, 230 m alt., 04 Mar 2016, van der Burgt 1940 (holotype: K; isotype: P, YA, Z).

Habitat

On rocks in streams.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Inversodicraea xanderi is not listed on http://www.iucnredlist.org. The taxon is currently known only from Campo. The extent of occurrence is estimated at 4 km2, and the area of occupancy is also about 4 km2. No major threat is known from the locality where the species occurs, therefore, I. xanderi is currently assessed as Near Threatened. IUCN Red List Category: Near Threatened (NT).

Ledermanniella aloides (Engl.) C.Cusset, Adansonia sér. 2, 14(2): 273 (1974)

Inversodicraea aloides Engl., Veg. Erde 9(3, 1): 271 (1915)

Type

Cameroon, Tschape pass, near Tchabal Mbabo, Ledermann 2785 (lectotype: B; isotype: U).

Specimens examined

Nigeria, Butum River, Keay FHI 25150; Utanga, Butum River, Keay FHI 25153; Tschape pass, near Tchabal Mbabo, Ledermann 2785 (U).

Habitat

On rocks in river.

Distribution

Cameroon (Fig. 25) and Nigeria.

Conservation status in Cameroon

Ledermanniella aloides has been assessed globally as Vulnerable by Diop (2010a). Onana and Cheek (2011) assessed this taxon for Cameroon as Endangered. The taxon is known from one locality. The extent of occurrence, and the area of occupancy are both estimated at 4 km2 each. Based on the area of occupancy, the number of localities and the agricultural development impact in the area, L. aloides is here reassessed and maintained as Endangered. IUCN Red List Category: Endangered EN B2ab (iii).

Ledermanniella batangensis (Engl.) C.Cusset, Adansonia sér. 2, 14(2): 273 (1974)

Dicraeia batangensis Engl., Bot. Jahrb. Syst. 43(4): 380 (1909)

Inversodicraeia batangensis Engl., Veg. Erde 9(3, 1): 271 (1915)

Type

Cameroon, Grand Batanga, Ledermann 221 (holotype: B). Basionym: Dicraeia batangensis Engl., Bot. Jahrb. Syst. 43(4): 380 (1909).

Specimen examined

Grand Batanga, Lobe waterfalls, Ledermann 221 (holotype: B, isotype: U).

Habitat

On rocks in waterfalls.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Ledermanniella batangensis is listed on http://www.iucnredlist.org globally as Critically Endangered (Ghogue 2010d). Onana and Cheek (2011) also assessed this species as Critically Endangered. The taxon is known from only Lobe waterfalls. The area of occupancy and extent of occurrence are both estimated at 4 km2. The locality has a booming tourist industry and this has led to a general decline in quality of the habitat of the species. L. batangensis is here reassessed and the earlier assessment is maintained as Critically Endangered. IUCN Red List Category: Critically Endangered B1ab (ii, iii) +2ab (ii, iii).

Ledermanniella bifurcata (Engl.) C.Cusset, Adansonia sér. 2, 14(2): 273 (1974)

Inversodicraea bifurcata Engl., Veg. Erde 9(3, 1): 273 (1915)

Type

Cameroon, Kribi, Mildbraed 5951 (holotype: B).

Specimens examined

Bipindi, Annet 321 (P); 10 km from Kribi-Lolodorf, Kienke rapids, J.J. Bos 7071, 7072 (WAG); 33 km northeast of Eta, 60 km southeast of Ngoila, Nki waterfalls, R. Letouzey 11949 (P); 50 km east of Grand Batanga, Kribi waterfalls, Mildbraed 5951, 5952, 5952a (YA).

Habitat

River rapids and waterfalls in evergreen forests.

Distribution

Cameroon (Fig. 25), Gabon, Congo, Equatorial Guinea.

Conservation status in Cameroon

Ledermanniella bifurcata has been assessed globally as Vulnerable (Ghogue 2010e). The taxon is known from 6 localities. The extent of occurrence of L. bifurcata is about 11,166 km2 and the area of occupancy is about 24 km2. The main threats currently known from the localities are forest logging and agriculture. Based on these threats, the number of localities currently known, and the continuous decline of vegetation cover in the area, extent and /or quality of habitat, L. bifurcata is currently reassessed as Vulnerable. IUCN Red List Category: Vulnerable VUB1+2ab (iii).

Ledermanniella keayi (G.Taylor) C.Cusset, Adansonia sér. 2, 14(2): 274 (1974)

Inversodicraea keayi G.Taylor; Bull. Brit. Mus. (Nat. Hist.) Bot. 1: 78 (1953)

Type

Cameroon, Kumbo, Keay FHI 28457 (holotype: K).

Specimens examined

Cameroon: Banso, Bamenda, Keay FHI 28457 (YA); near Sagbo, Ndop near Bamenda, 1800 m alt., C. D. Adams 11073 (LISC); Kumbo, 1650 m alt., Keay FHI 28457 (K).

Habitat

River rapids.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Ledermanniella keayi is listed on http://www.iucnredlist.org as Critically Endangered (Diop 2010b). The taxon is known from one locality, restricted to a small area in an agricultural landscape. The extent of occurrence and the area of occupancy are both estimated at 2 km2 each. The earlier assessment is here maintained as Critically Endangered. IUCN Red List Category: Critically Endangered CRB2ab (iii).

Ledermanniella letouzeyi C.Cusset, Bull. Mus. Natl. Hist. Nat., B, Adansonia Sér. 4, 6(3): 260. (1985)

Type

Cameroon, near Lokando, Mount Rumpi, Ure, 23 Mar 1976, R. Letouzey 14517 (YA).

Specimen examined

30 km northwest of Kumba, near Lokando, Mount Rumpi, Ure, on river, Mar, R. Letouzey 14517 (holotype P, isotype YA).

Habitat

River rapids and waterfalls in tropical forests.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Ledermanniella letouzeyi is listed on http://www.iucnredlist.org. The taxon was assessed as Endangered by Cheek (2004). Onana and Cheek (2011) maintained the Endangered status of Cheek (2004). The species is known from two localities. The extent of occurrence is estimated at 4 km2 and the area of occupancy is about 8 km2. The main threats in the locality are forest exploitation and agriculture. The earlier assessment by Cheek (2004) and Onana and Cheek (2011) is maintained. IUCN Red List Category: Endangered ENB2ab (iii).

Ledermanniella linearifolia Engl., Bot. Jahrb. Syst. 43(4): 378 (1909)

Sphaerothylax linearifolius Engl., Veg. Erde 9(3, 1): 275 (1915)

Type

Cameroon, 28 Aug 1908, C. Ledermann 440 (YA).

Specimens examined

7 km south of Kribi, Lobe waterfall, Jan, J. Bos3591 (K); 7 km south of Kribi, Lobe waterfalls, Aug, De Wild 2876 (P, WAG, YA); Nkam, near Sahe, 3 km southwest Nkondjok road Bafang-Yabassi, Feb R. Letouzey 11146 (P).

Habitat

River rapids and waterfall.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Ledermanniella linearifolia is listed on http://www.iucnredlist.org. It was assessed as Endangered (Ghogue 2010f). Onana and Cheek (2011) reassessed this species and maintained the Endangered status. The taxon is known from 6 localities. The extent of occurrence of L. linearifolia is about 42,848,649 km2 and the area of occupancy is about 16 km2. The main threats currently known from the localities are agriculture and touristic activities. Based on these threats, the number of localities currently known, and the continuous decline of vegetation cover in the area, extent and /or quality of habitat, L. linearifolia is currently reassessed and maintained as Endangered. IUCN Red List Category: Endangered ENB2ab (iii).

Ledermanniella monandra (Engl.) C.Cusset, Adansonia, sér., 2, 14(2): 274 (1974)

Monandriella linearifolia Engl., Bot. Jahrb. Syst. 60(4): 457 (1926)

Type

Cameroon, Mao Bika, near Dodeo, 05 Mar 1909, C. Ledermann 2872 (YA).

Specimen examined

Mao Bika, near Dodeo, 60 km west of Tignere, 700 m alt., Mar, Ledermann 2872 (holotype B).

Habitat

River rapids.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Ledermanniella monandra has not yet been assessed for the IUCN Red List, but it was assessed in Onana and Cheek (2011). The taxon is known from one locality. The extent of occurrence and the area of occupancy are estimated at 4 km2 each. Due to habitat degradation and the continuous decline of vegetation cover in the area, extent and /or quality of habitat, L. monandra is currently reassessed as Critically Endangered. IUCN Red List category: Critically Endangered CRB2ab (iii).

Ledermanniella musciformis (G.Taylor) C.Cusset, Adansonia ser 2 14(2): 274 (1974)

Inversodicraea musciformis G.Taylor; Bull. Brit. Mus. (Nat. Hist.) Bot. 1: 75 (1953)

Type

Cameroon, Mba Kokeka, near Bamenda, Jan, Keay FHI 28542 (holotype: K). Basionym: Inversodicraea musciformis G.Taylor; Bull. Brit. Mus. (Nat. Hist.) Bot. 1: 75 (1953).

Specimens examined

Northwest slopes of Mts. Mba Kokeka, near Bamenda, Jan, Keay FHI 28542 (K); Tchamba, Nakalba, 21 km southwest of Tchamba 1200 m alt., Jan, J. & A. Raynal 13166 (P).

Habitat

River rapids and waterfalls.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Ledermanniella musciformis is listed on http://www.iucnredlist.org as Data Deficient (Diop 2010c). Onana and Cheek (2011) reassessed this species as Endangered. This taxon is endemic to Cameroon and known from at least four localities. The extent of occurrence of L. musciformis is about 68,419,636 km2 and area of occupancy is about 16 km2. The main threat currently known from the localities is deforestation and agriculture. Based on these threats, the number of localities, and the continuous decline of vegetation cover in the area, extent and/or quality of habitat, L. musciformis is currently reassessed and Endangered status maintained. IUCN Red List Category: Endangered ENB2ab (iii).

Ledermanniella onanae Cheek, Kew Bull. 58: 733 (2003)

Type

Cameroon, Bakossi Mts, northwest of Muambong, 04 Feb 1998, J.-M. Onana 558 (K, YA).

Specimens examined

Cameroon: South West Province, Bakossi Mts., Chide River falls, northwest of Muambong, 04 Feb 1998, J.-M. Onana 558 (YA, K); South West Province, Bakossi Mts., Ndip River rapids between Nzimbeng and Kodmin, alt. 1150 m. fl. & fr., 14 Feb 1998, M. Cheek 9196 (K, YA).

Habitat

Perennial waterfalls and river rapids in submontane forest.

Distribution

Cameroon (Fig. 25) and Gabon.

Conservation status in Cameroon

Ledermanniella onanae is listed on http://www.iucnredlist.org as globally Endangered (Ghogue 2010g). Onana and Cheek (2011) maintained the Endangered status. The taxon is known from three localities, two of which are on the same river. The extent of occurrence of L. onanae is about 23,751 km2 and the area of occupancy is about 12 km2. The main threats currently known from the localities are forest logging and agriculture. Based on these threats, and the continuous decline of vegetation cover in the area, extent and /or quality of habitat, L. onanae is currently reassessed and the Endangered status maintained. IUCN Red List Category: Endangered ENB2ab (iii).

Ledermanniella pollardiana Cheek & Ameka, Nordic J. Bot. 26: 214 (2008)

Type

Cameroon, North Western Province, Bali, 1 km east, 5°52'N, 10°01'E, 19 Nov 2000, B. Pollard 536 (K, YA).

Specimens examined

Cameroon, North-western Province, Bali, 1 km east, 5°52'N, 10°01'E, 1280 m alt. fl., 19 Nov 2000, B. Pollard 536 (K, YA).

Habitat

Perennial waterfall, in full sun, in deforested area.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Ledermanniella pollardiana is not as yet assessed for the IUCN Red List. Onana and Cheek (2011) assessed this species as Critically Endangered. The taxon is endemic to Cameroon, and known from only the type locality. The extent of occurrence and the area of occupancy are both estimated at 4 km2 each. Agricultural activities in the general area of the locality; with increased turbidity and siltation from agricultural practices will adversely affect the species. The species is here reassessed and Critically Endangered status maintained. IUCN Red List Category: Critically Endangered CRB2ab (iii).

Ledermanniella prasina J.J.Schenk & D.W.Thomas, Novon 14(2): 227 (2004)

Type

Cameroon, 01 Dec 1990, D.W. Thomas 11550 (K, WAG, YA).

Specimen examined

Cameroon, 01 Dec 1990, D.W. Thomas 11550, [K, WAG, YA].

Habitat

River rapids.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Ledermanniella prasina was assessed as Vulnerable (Cheek 2017b) for the IUCN Red List. The taxon is known only from the Mana River valley system in Cameroon. The extent of occurrence and the area of occupancy are both estimated at 2 km2 each. The assessment of Cheek (2017b) is maintained since no major changes have taken place at the locality since that assessment. The species is here reassessed as Vulnerable. IUCN Red List Category: Vulnerable VUB1+2ab (iii).

Ledermanniella pusilla (Warm.) C.Cusset, Adansonia ser. 2, 14(2): 274 (1974)

Dicraeanthus pusillus C.H.Wright, Fl. Trop. Afr. 6(1.1): 127 (1909)

Sphaerothylax pusilla Warm Kongel. Danske Vidensk. Selsk. Skr., Naturvidensk. Math. Afd. VI, 9: 146 (1899)

Type

Cameroun, Bipindi, G. Zenker 1050 (holotype: B; isotype: G). Basionym: Sphaerothylax pusilla Warm., Kongel. Danske Vidensk. Selsk. Skr., Naturvidensk. Math. Afd. VI, 9: 146 (1899).

Specimens examined

7 km south of Kribi, Lobe waterfall, J.J. Bos 3598 (WAG); Lokoundje waterfall, Bipindi, G. Zenker 1050 (G, K, L, M, U, Z).

Habitat

Waterfalls.

Distribution

Cameroon (Fig. 25), Democratic Republic of Cong and Gabon.

Conservation status in Cameroon

Ledermanniella pusilla is listed on http://www.iucnredlist.org globally as Endangered (Ghogue 2010h). The taxon is known from two localities. The extent of occurrence is about 9,042 km2 and the area of occupancy is about 16 km2. The waterfalls at Lobe are a huge tourist center and the activities have caused a deterioration in the habitat of the species. The species is here reassessed as Endangered. IUCN Red List Category: Endangered ENB1 + 2ab (iii).

Ledermanniella sanagaensis C.Cusset, Bull. Mus. Natl. Hist. Nat. B, Adansonia Sér. 4, 6(3): 256 (1985)

Type

Cameroon, Natchigal, J. & A. Raynal 10543 (YA).

Specimens examined

Cameroon, J. & A. Raynal 10543 (YA); Natchigal, Sanaga waterfall, A. & J. Raynal 10542 (P).

Habitat

River rapids and waterfalls.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Ledermanniella sanagaensis is listed on http://www.iucnredlist.org as Critically Endangered (Ghogue 2010i). The taxon is endemic to Cameroon, and known only from the Sanaga waterfall at Natchigal. The extent of occurrence and area of occupancy are both estimated at 4 km2 each. There is a proposal to build a dam at the locality of the species. Based on this threat the earlier assessment of Ghogue (2010i) as Critically Endangered is maintained. IUCN Red List Category: Critically Endangered B2ab (ii, iii).

Ledermanniella schlechteri (Engl.) C.Cusset, Adansonia sér., 2, 14(2): 275 (1974)

Dicraeia schlechteri Engl., Bot. Jahrb. Syst. 43: 381 (1909)

Inversodicraeia tenuissima Hauman, Bull. Jard. Bot. État 17: 180 (1944)

Type

Congo Democratic Republic, 01 Jun 1899, R. Schlechter12574 (K). Basionym: Dicraeia schlechteri Engl., Bot. Jahrb. Syst. 43: 381 (1909).

Specimens examined

Dehane, between Edea and Kribi, Jun, Annet 459 (P).

Habitat

River rapids and waterfalls.

Distribution

Cameroon (Fig. 25), Congo and Democratic Republic of Congo.

Conservation status in Cameroon

Ledermanniella schlechteri is listed on http://www.iucnredlist.org as Vulnerable, globally (Ghogue 2010j). The taxon is known from two localities. The extent of occurrence is less than 100 km2, and the area of occupancy is about 8 km2. The proposed dam at Edea waterfall will further deteriorate the quality of the habitat of the species at that locality. Base on this threat and the number of localities where the species is currently found, L. schlechteri is here reassessed as Endangered. IUCN Red List Category: Endangered ENB1+2ab (iii).

Ledermanniella thalloidea (Engl.) C.Cusset, Adansonia sér 2, 14(2): 275 (1974)

Inversodicraeia thalloidea Engl., Veg. Erde 9(3, 1): 274 (1915)

Type

Cameroon, Ndoungue near Nkongsamba, Ledermann 6328a (lectotype: B; isotypes: BM, U). Basionym: Inversodicraeia thalloidea Engl., Veg. Erde 9(3, 1): 274 (1915).

Specimens examined

Tributary of Sanaga, 10 km north of Edea, Kers 1904 (LISC); Ndoungue near Nkongsamba, 800 m alt., Ledermann 6328a (BM, U); Natchigal, Sanaga waterfall, A. & J. Raynal 10542 (P).

Habitat. River rapids and waterfalls in tropical rain forest.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Ledermanniella thalloidea is listed on http://www.iucnredlist.org as Endangered (Ghogue 2010k). However, Onana and Cheek (2011) assessed the taxon as Vulnerable. The taxon is endemic to Cameroon and known from two localities. The species’ area of occupancy is estimated to be less than 10 km2, and the extent of occurrence estimated at 18 km2. There is a decline in the quality of the habitat of the species; there is a dam at the Sanaga waterfalls, and another dam construction is in progress at the Nachtigal waterfalls, the two sites for the species. Due to the impact of the dams on the habitat of the species it is here reassessed as Critically Endangered. IUCN Red List Category: Critically Endangered CRB2ab (iii).

Ledermanniella raynaliorum C.Cusset, Bull. Mus. Natl. Hist. Nat. B, Adansonia Ser. 4, 6(3): 264 (1985)

Type

Cameroon, 14 Jan 1965, J. & A. Rayanal 12988 (YA).

Specimen examined

Cameroon, 14 Jan 1965, J. & A. Rayanal 12988 (YA).

Habitat

River rapids.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Ledermanniella raynaliorum is not listed on http://www.iucnredlist.org. Onana and Cheek (2011) assessed this species as Endangered. The taxon is known from only one locality. The extent of occurrence and the area of occupancy are estimated at about 4 km2 each. Forest degradation is the main threat at the locality. The species is here assessed as Near Threatened. IUCN Red List Category: Near Threatened (NT).

Ledermanniella variabilis (G.Taylor) C.Cusset, Adansonia sér 2, 14(2): 275 (1974)

Inversodicraeia variabilis G.Taylor, Bull. Brit. Mus. (Nat. Hist.) Bot. 1: 75 (1953)

Type

Cameroon, Manfe, Munaya, Keay FHI 28688, (holotype: K). Basionym: Inversodicraeia variabilis G.Taylor, Bull. Brit. Mus. (Nat. Hist.) Bot. 1: 75 (1953).

Specimens examined

Lobe waterfall, 7 km south of Kribi, J.J. Boss 3594 (WAG); Mamfe, Munaya River, Keay FHI 28688 (K).

Habitat

River rapids and waterfalls.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Ledermanniella variabilis is listed on http://www.iucnredlist.org as Endangered (Ghogue 2010l). Onana and Cheek (2011) reassessed this species as Endangered. The species is known from two localities and the area of occupancy and extent of occurrence are estimated to be less than 10 km2 each. The Lobe waterfall locality is a famous tourist attraction so there is a continuous decline in the quality of the habitat at this site. The species is here reassessed as Critically Endangered. IUCN Red List Category: Critically Endangered CRB1+2ab (ii, iii).

Leiothylax quangensis Warm., Danske Vid. Selsk. Skrift. Ser.. VI, 9: 147 (1899)

Dicraeia quangensis Engl., Bot. Jahrb. Syst. 20(1–2): 134 (1894)

Leiocarpodicraea buesgenii Engl., Engl. Bot. Jahrb. Syst. 60: 465 (1926)

Leiothylax buesgenii Warm. ex Engl., Nat. Pflanzenfam. 18 a ed. 2, 58 (1930)

Leiothylax edeensis Engl. Nat. Pflanzenfam. 18 a ed. 2, 58 (1930)

Type

Democratic Republic of Congo, Teuscz in von Mechow’s Expedition 506 (holotype: M; isotype: G).

Specimens examined

Edea, Sanaga waterfall, Buesgen 439 (M); Sanaga waterfall, Buesgen s.n. (B, U).

Habitat

River rapids and waterfalls in tropical rain forests.

Distribution

Angola, Cameroon (Fig. 25), Democratic Republic of Congo.

Conservation status in Cameroon

Leiothylax quangensis has been assessed for the IUCN Red List as Endangered (Ghogue 2010m). The taxon is known from one locality, Edea waterfalls. The area of occupancy and extent of occurrence are both estimated at 2 km2 each. The hydropower dam at Edea will certainly impact the quality of the habitat of the species. L. quangensis is here reassessed as Critically Endangered. IUCN Red List Category: Critically Endangered CRB1+2ab (ii, iii).

Letestuella tisserantii G.Taylor, Bull. Brit. Mus. (Nat. Hist.) Bot. 1: 57 (1953)

Letestuella chevalieri G.Taylor, Bull. Brit. Mus. (Nat. Hist.), Bot. 1: 59 (1953)

Leiothylax warmingii (Engl.) Warm., Danske Vid. Selsk. Skrift. Ser. VI. ix 150 (1899)

Type

Central African Republic, Tisserant 1769 (holotype: BM; isotype: P).

Specimens examined

Near Goyoum in Sanaga River, 20 km west of Deng Deng, F.J. Breteler 981 (WAG); Plateau de l’Adamaoua, Vina waterfall, 15 km from Ngaoundere, Zehnder 163 (ZT).

Habitat

River rapids and waterfalls in tropical rain forest.

Distribution

Benin, Cameroon (Fig. 25), Central African Republic, Mali, Namibia and Niger.

Conservation status in Cameroon

Letestuella tisserantii is listed on http://www.iucnredlist.org as Least Concern (Diop 2010d) since it occurs in many countries. The taxon is known from two localities in Cameroon. The extent of occurrence is less than 100 km2, and the area of occupancy is less than 10 km2. Dams on the Sanaga River and agricultural activities are the main threats to the species. Based on the threats and the number of localities where the species is found, L. tisserantii is here assessed as Endangered. IUNC Red List Category: Endangered ENB2ab (iii).

Macropodiella heteromorpha (Baill.) C.Cusset, Adansonia, sér. 2, 17(3): 298 (1978)

Sphaerothylax heteromorpha Baill., Bull. Mens. Soc. Linn. Paris ii 876 (1890)

Macropodiella mildbraedii Engl., Bot. Jahrb. Syst. 60(5): 466 (1926)

Type

Gabon, Thollon 729 (holotype: P). Basionym: Sphaerothylax heteromorpha Baill., Bull. Mens. Soc. Linn. Paris ii 876 (1890).

Specimens examined

Makak Forest Reserve, P. Bamps 1453 (YA); Nyong River, near Mbalmayo, Mildbraed 7749, 7750 (B, U).

Habitat

River rapids and waterfalls in tropical rainforests.

Distribution

Cameroon (Fig. 25), Côte d’Ivoire and Gabon.

Conservation status in Cameroon

Macropodiella heteromorpha is listed on http://www.iucnredlist.org as Vulnerable (Ghogue 2010n). The taxon is known from four localities, and the area of occupancy is less than 500 km2 and the extent of occurrence estimated at 75 km2. At one of the localities (Meve’ele waterfalls) it is proposed to build a hydropower dam. The species is threatened by habitat decline due to future dam construction. According to Ghogue (2010n) two other localities, Nyong River near Mbalmayo and the Mpoume waterfalls on the Nyong River near Makak, have been listed by Cusset (1987) for this species. These two sites have been surveyed by Ghogue but the species has not been seen or collected. M. heteromorpha is, therefore, here reassessed as Critically Endangered. IUCN Red List Category: Critically Endangered CRB2ab (ii, iii).

Macropodiella pellucida (Engl.) C.Cusset, Fl. Cameroun 30: 64 (1987)

Type

Cameroon, Bare, near Nkongsamba, Ledermann 6142 (lectotype: BM). Basionym: Inversodicraea pellucida Engl., Veg. Erde 9(3, 1): 271, 272. (1915).

Specimens examined

Bare, near Nkongsamba, on rocks in a waterfall, Ledermann 6142 (BM); Ndian River, near Mundemba, Dec, D.W. Thomas 2552 (MO, P).

Habitat

River rapids and waterfalls in rainforest.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Macropodiella pellucida is listed on http://www.iucnredlist.org as Endangered (Ghogue 2010o). Onana and Cheek (2011) maintained the Endangered status of Ghogue (2010o). The taxon is endemic to Cameroon and known from two localities. The extent of occurrence is less than 4 km2 and the area of occupancy of this species is estimated at less than 20 km2. There have not been further threats at the habitat of the species since the previous assessment. The species is reassessed as Endangered, maintaining the previous status. IUCN Red List Category: Endangered ENB2ab (iii).

Saxicolella flabellata (G.Taylor) C.Cusset, Fl. Cameroun 30: 94 (1987)

Pohliella flabellata G.Taylor, Bull. Brit. Mus. (Nat. Hist.), Bot. 1: 53 (1953)

Type

Nigeria, Afi River, Dec, Keay FHI 28240 (K). Basionym: Pohliella flabellata G.Taylor, Bull. Brit. Mus. (Nat. Hist.), Bot. 1: 53 (1953).

Specimens examined

Nigeria: Afi River, on Aboabam-Boje path, Dec, Keay FHI 28240 (K); Cameroon: Ndian, near Mundemba, D.W. Thomas 2654 (MO, P).

Habitat

Submerged on rocks in fast-flowing river.

Distribution

Cameroon (Fig. 25) and Nigeria.

Conservation status in Cameroon

Saxicolella flabellata is list on http://www.iucnredlist.org. The taxon has been assessed as Data Deficient (Ouedraogo 2010a) since species distribution, population status and threats to the species are unknown at the time of the assessment. Onana and Cheek (2011) reassessed the species as Endangered. The species is found in two localities. The extent of occurrence is estimated at 2 km2 and the area of occupancy is about 8 km2. The main threats at the localities are described as forest exploitation and agriculture. The species is here reassessed as Endangered. IUCN Red List Category: Endangered ENB2ab (iii).

Saxicolella laciniata (Engl.) C.Cusset, Fl. Cameroun 30: 94 (1987)

Inversodicraea laciniata Engl., Veg. Erde 9(3, 1): 271 (1915)

Pohliella laciniata Engl., Bot. Jahrb. Syst. 60(4): 458 (1926)

Type

Cameroon, near Babong, Ledermann 1185 (holotype: B). Basionym: Pohliella laciniata Engl., Bot. Jahrb. Syst. 60(4): 458 (1926).

Specimens examined

Dinger River near Babong, Ledermann 1185 (B); Bawan River, on path to Agborkem (ex Ossidinge) at Tabo, 20 km west of Mamfe, R. Letouzey 13731 (YA).

Habitat

River rapids.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Saxicolella laciniata is listed on http://www.iucnredlist.org as Vulnerable (Ghogue 2010p). It was assessed in Onana and Cheek (2011) as Endangered. The taxon is known from two localities. The extent of occurrence is estimated at 2 km2 and the area of occupancy is 8 km2. The main threats at the localities are forest exploitation for agriculture purposes. The species is here reassessed and the Endangered status maintained. IUCN Red List Category: Endangered ENB2ab (iii).

Saxicolella marginalis (G.Taylor) C.Cusset ex Cheek, Pl Mount Oku & Ijim Ridge, Cameroon, Conserv. Checklist 153 (2000)

Butumia marginalis G.Taylor, Bull. Brit. Mus. (Nat. Hist.) Bot. 1: 55 (1953).

Type

Nigeria, 25 Dec 1948, Keay, Savory & Russell, #25152 (BM). Basionym: Butumia marginalis G.Taylor, Bull. Brit. Mus. (Nat. Hist.) Bot. 1: 55 (1953).

Specimens examined

Nigeria: Butum River, Utanga, 2 miles north of Bagga, Obudu, 25 Dec 1948, Keay, Savory & Russell FHI 25152 (YA); Cameroon: Fundong, 22 Nov 1996, M. Cheek 8740 (YA).

Habitat

On smooth granite rocks in swift-flowing stream or river.

Distribution

Cameroon (Fig. 25) and Nigeria.

Conservation status in Cameroon

Saxicolella marginalis is listed on http://www.iucnredlist.org. The taxon has been assessed globally as Critically Endangered (Ouedraogo 2010b). There is only one known collecting locality in the country. According to Ouedraogo (2010b) there is decline in the quality of the habitat due to pollution from laundry operations in the town of Fundong upstream of the site of this species. Based on this threat the assessment of Critically Endangered is maintained. IUCN Red List Category: Critically Endangered B1ab (iii) +2ab (iii).

Saxicolella nana Engl., Bot. Jahrb. Syst. 60(4): 456 (1926)

Type

Cameroon, near Mbalmayo, Mildbraed 7749a (holotype: B; isotype: U).

Specimens examined

Cameroon, near Mbalmayo, Nyong River, 644 m alt, Mildbraed 7749a (YA); 11°27'N, 3°22'E, 28 Feb 2007, M. Kato, R. Imaichi, S. Koi, & N. Katayama CMR-129 (YA).

Habitat

River rapids and waterfalls.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Saxicolella nana is listed on http://www.iucnredlist.org as Vulnerable (Ghogue 2010q). Onana and Cheek (2011) assessed this species as Critically Endangered, since at that time it had not been collected since the first collection many years ago. The taxon is endemic to Cameroon and is known from only Nyong River near Mbalmayo. The species was, however, collected again by Kato and associates in 2007. The area of occupancy of this species can be estimated to be less than 20 km2. The extent of occurrence -estimated to be less than 2 km2. The main threat is agricultural activity. The species is here reassessed as Endangered. IUCN Red List Category: Endangered ENB2ab (ii, iii).

Stonesia ghoguei E.Pfeiter & Rutish., Novon 19(1): 103 (2009)

Type

Cameroon, Adamawa, Ngaoundere, 16 Feb 2005, J. P. Ghogue 1665 (YA, K, Z).

Specimens examined

Adamawa, Ngaoumdere, Tello Waterfalls, 16 Feb 2005, J. P. Ghogue 1665 (YA, K, Z).

Habitat

Growing in waterfalls, Tello Waterfalls, Ngaoundéré, Adamawa (Cameroon).

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Stonesia ghoguei is listed on http://www.iucnredlist.org as Vulnerable (Cheek 2018). Pfeifer et al. (2009) assessed S. ghoguei as Vulnerable. The taxon is endemic to Cameroon and known from only one collecting locality, Tello Waterfalls. The extent of occurrence and area of occupancy are estimated at 4 km2 each. Their assessment is retained for now. IUCN List Category: Vulnerable VU D1 + 2.

Tristicha trifaria (Bory ex Willd.) Spreng., Systema Vegetabilium 1 (1824)

Dufourea boryi A.Rich., Dict. Class. Hist. Nat. 5: 636 (1824)

Dufourea hypnoides St-Hil. Mém. Mus. Hist. Nat. 10: 472 (1823)

Dufourea trifaria Bory ex Willd., Sp. Pl., ed. 4 5(1): 55 (1810)

Dufourea alternifolia Willd., Mag. Neuesten Entdeck. Gesammten Naturk. Ges. Naturf. Freunde Berlin 6: 64 (1812)

Tristicha alternifolia Thouars ex Spreng., Syst. Veg. ed. 16(1): 22 (1824)

Tristicha alternifolia Thouars, ex Roem. & Schult. Syst. Veg. i. 50 (1817)

Type

Mauritius, Bory de St Vincent s.n. (holotype: B; isotype: P).

Specimens examined

8 km south of Kribi, Lobe waterfall, J.J. Bos 3593 (YA); Vina waterfall, near Ngaoundere, Feb, Dulieu 5 (ALF); Hossere Koum, 40 km west of Tchollire, Nov, Fotius 2418 (P); Limbe (Joke River), Mar, Brenen 9495, 9496 (BR, COL, P, SRGH); 8 km North Betare Oya (Mari River fall), Nov, Leeuwenberg 7767 (P, WAG); Roua 20 km northeast of Mokolo, Oct, R. Letouzey 7280 (P); Sahe, 3 km southwest of Nkondjok (Bafang – Yabassi Road), Nkam River, Feb, R. Letouzey 11145 (P).

Habitat

River rapids and waterfalls.

Distribution

AFRICA; Angola, Benin, Burkina Faso, Cameroon (Fig. 25), Cote d’Ivoire, Democratic Republic of Congo, Ethiopia, Ghana, Guinea, Kenya, Liberia, Madagascar, Malawi, Mali, Mauritius, Mascarene Islands, Mozambique, Namibia, Niger, Nigeria, Senegal, Sierra Leone, South Africa, Sudan, Tanzania, Togo, Uganda, Zambia, Zimbabwe. CENTRAL AND SOUTH AMERICA; Argentina, Brazil, Columbia, Costa Rica, Cuba, El Salvador, Guatemala, Mexico, Nicaragua, Panama, Paraguay, Uruguay, Venezuela.

Conservation status in Cameroon

Tristicha trifaria is not listed on www.iucnredlist.org. The extent of occurrence of T. trifaria is about 12,000 km2 and the area of occupancy is about 28 km2. The taxon is currently known from about 7 localities. Lobe area, one of the localities where the species is found is a famous touristic site. Also agricultural activities are on the increase in other localities. Based on these threats, the number of localities and the continuous decline of vegetation cover in the area, extent and /or quality of the habitat, T. trifaria is here assessed as Vulnerable. IUCN Red List Category: Vulnerable VUB1 + 2ab (ii, iii).

Winklerella dichotoma Engl., Bot. Jahrb. Syst. 38(1): 97 (1905)

Type

Cameroon, Edea, 30 Jan 1951, Winkler 900 (holotype: B).

Specimens examined

Edea waterfall, Winkler 900 (B); Edea waterfall, 30 Jan 1951, Zehnder 271, 275, 277 (BR, ZT).

Habitat

River rapids and waterfalls.

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Winklerella dichotoma is list on http://www.iucnredlist.org as Critically Endangered (Ghogue 2010r). The species is endemic to Cameroon and only known from the Edea waterfalls on the Sanaga River. There is a hydropower dam built on the river at the collecting locality of the species. The area of occupancy and extent of occurrence are estimated at 2 km2 each. The earlier assessment of Ghogue (2010r) as Critically Endangered is maintained. IUCN Red List Category: Critically Endangered B1ab (iii) +2ab (iii).

Zehnderia microgyna C.Cusset, Fl. Cameroon 30: 56 (1987)

Type

Cameroon, Edea, 29 Jan 1951, Zehnder 264 (holotype: ZT).

Specimen examined

Edea, Sanaga waterfall, 29 Jan 1951, Zehnder 264, 276, 278 (ZT).

Distribution

Cameroon (Fig. 25).

Conservation status in Cameroon

Zehnderia microgyna is listed on http://www.iucnredlist.org. as Critically Endangered (Ghogue 2010s). The taxon is known from only one locality. The extent of occurrence of Z. microgyna and the area of occupancy are estimated at about 4 km2 each. There is a dam built on the Sanaga River, the habitat of the species. Based on that threat, and the fact that the species is known only from one locality and the continuous decline of vegetation cover in the area, and extent and/or quality of habitat, Z. microgyna is here assessed as Critically Endangered. IUCN Red List Category: Critically Endangered CRB1+2ab (ii, iii).

Discussion

The survey of rheophytic plants from Cameroon revealed 66 species distributed in 16 families, and in three major plant groups: 2 ferns, 8 monocotyledons, and 56 dicotyledons (Table 1). Among the monocotyledons only one grass and two sedges were recorded. Within the dicotyledons three shrub/small tree species, Deinbolla saligna Keay (Sapindaceae), Ixora euosmia K.Schaum (Rubiaceae) and Pandanus satabiei Huynh (Pandanaceae) were encountered (Table 1). According to van Steenis (1981), however, about half the species of rheophytes worldwide are trees and thus the paucity of trees in the current survey is surprising. Rheophytic woody plants (e.g., Coffea congensis Froehn and Breonadia salicina (Vahl) Hepper & Wood in the Rubiaceae) are known to occur outside the study area in Africa. Rheophyte diversity, according to some authors e.g., van Steenis (1981) and Hoyos-Gomez and Bernal (2018), is high in South East Asia and South America compared with tropical Africa. A survey of rheophytes of Africa by Ameka et al. (2002) found 53 rheophytes including 33 Podostemaceae species in Cameroon. This means that we have documented 10 more Podostemaceae and three other rheophytic species (from Cyperaceae: Cyperus rheophyticus, C. tonkinensis, and C. cataractarum) for Cameroon within the last 16 years. Further surveys are required across Africa for the full picture of rheophyte diversity and distribution to emerge.

Number of rheophyte species and genera per family in Cameroon.

Family Genus Species
Ferns
Lomariopsidaceae 1 2
Dicotyledons
Acanthaceae 1 1
Amaranthaceae 1 1
Apocynaceae 1 1
Lamiaceae 1 1
Myrtaceae 1 1
Oxalidaceae 1 2
Podostemaceae 12 43
Rubiaceae 2 4
Sapindaceae 1 2
Monocotyledons
Amaryllidaceae 1 1
Araceae 1 1
Cyperaceae 2 3
Melastomataceae 1 1
Pandanaceae 1 1
Poaceae 1 1

Invariably, the species encountered in the study have characteristic features that adapt them to their peculiar habitats, and enable them to persist in the harsh conditions of swift-flowing water, flush floods, torrents, and waterfalls. The leaves are lanceolate or narrow with a leaf index of at least 3 similar to what van Steenis (1978, 1981) observed while studying the rheophytes of the world. Crinum natans and some other hydrophytes usually have ribbon-like leaves. The rheophytes encountered in Cameroon have firm but flexible stems which can withstand the tearing effect of swift-running rivers and streams. Their roots are strong or mat-rooted to hold them to their various substrates including rocks, gravel and boulders.

The habitats of this unique biological group are, however, threatened by human activities. We show that about 36% of rheophytes are Critically Endangered (CR) in Cameroon and only 2% are considered to be of Least Concern (Fig. 26). Fifty three percent of Podostemaceae in Cameroon are in the CR group. There is the need to do more to protect the habitats of the rheophytes, particularly the Podostemaceae in Cameroon.

Figure 26. 

Percent distribution of rheophytes of Cameroon according to IUCN Red List Categories (CR-Critically Endangered; EN- Endangered; LC- Least Concern; NT- Near Threatened; and VU- Vulnerable).

The habitats of rheophytes in Cameroon and indeed across Africa are threatened by the land use practices around the rivers, and the damming of the rivers for hydroelectric power (Cheek et al. 2015). One such land use practice, agriculture (arable farming), introduces agro-chemicals and silt to the rivers. This may make the river turbid, thus affecting photosynthetic ability and therefore the productivity of the plants (Ameka 2000). The agro-chemicals may also poison the plants. Timbering loosens the topsoil and during the wet season run-off water carries silt into the rivers; and the effect is the same as for silt from arable farming (Ameka pers. obs.) – turbid water which results in reduced productivity of submerged water plants. Mining is another land use practice affecting the plants and in particular alluvial mining in rivers may contribute silt into the rivers as suggested by Cheek et al. (2015) and Cheek and Lebbie (2018). The amount of silt from alluvial mining could be much higher than from agriculture because that from alluvial mining is generated in-situ, in the riverbed and, therefore, the effect may be more severe. Silt not only reduces photosynthesis efficiency but may also reduce or even prevent establishment of seedlings of rheophytes on rocks, particularly the members of Podostemaceae (Cheek et al. 2015). In some instances heavy metals such as mercury are used in the recovery of alluvial gold (Afum and Owusu 2016) and these may poison the plants. Indeed Philbrick and Crow (1983) and Philbrick and Novelo (1995) have provided evidence to show that there is a correlation between increased pollution (chemicals) and loss of Podostemaceae populations in South America.

The recent upsurge in dam construction effort in many African countries raises concern for the survival of rheophytes. In Cameroon, there are a number of dams built across rivers for hydropower, and efforts are continuing to build many more dams across a number of rivers: (http://www.theworldfolio.com/news/hydroelectric-projects/659/eroon); examples of these are:, Memve’élé hydroelectric dam on Ntem River(http://www.edennewspaper.net/memveele-hydroelectric-dam-is-60-complete-energy-minister/); Mekin hydro-electric dam on Dja River, Lom-Pangar hydroelectric dam on Lom River (https://www.internationalrivers.org/sites /default/files/attached-files/lp_factsheet.pdf); Menchum hydroelectric dam on Menchum River, and the Natchigal hydroelectric dam on Sanaga Rive1r at Edea; http://www.hydroworld. com/ articles/2013/11/cameroon-makes-deal-for-330-mw-nachtigal-falls-hydropower-project. html; and https://afrique.edf.com/en/edf-in-africa/news/a-new-phase-for-the-nachtigal-hydroelectric -project).

River rapids, cataracts, and waterfalls, are usually the preferred sites for dam construction for hydro-electric power, and also the habitats for many rheophytes, particularly the Podostemaceae. The rheophytes have become permanently submerged upstream of the dam due to flood water. The plants downstream are subjected to a different threat, that is, the change in flow rate and absence of flash floods below the dam (Cheek et al. 2015). In Ghana, two collecting localities of Tristicha trifaria (Podostemaceae) on the Volta River are now under lake water. Before the construction of the Akosombo dam on the Volta River in 1965, T. trifaria was collected at Kpando upstream of the dam. A second dam on the Volta River, down-stream of the Akosombo dam, was completed in 1982. T. triticha was collected on rocks in the river rapid just north of the Akuse dam (Ameka 2000). These two collecting sites have been lost because of the localities are permanently submerged (Ameka 2000). Thus dams threaten and /or endanger the very existence of rheophytic plants. We wish to draw attention to the threats posed by alluvial mining and dam construction to the survival of rheophytes and call on conservationists to do more to curb the indiscriminate damming of rivers, and alluvial mining across Africa. They must engage with policy makers in government and suggest alternative livelihoods for alluvial mine workers; and alternative green energy sources e.g., biofuels, biogas, and solar, instead of dam construction for hydropower.

Acknowledgements

We would like to thank the many individuals who have helped in diverse ways to enable the completion of this study. The contribution of those who helped in the field work is hereby acknowledged. Special thanks also go to the Director of the National Herbarium of Cameroon (YA) for the use of herbarium facilities. We thank the staff of the Plant Systematic and Ecology Laboratory of the Higher Teacher Training College for their assistance while doing this work. The support of Dr. Atanga Ekobo, former coordinator of WWF-CFP Limbe, for this study is highly appreciated. Dr Martin Cheek, Royal Botanic Gardens, Kew is thanked for his helpful comments on an earlier draft of this paper. Finally, we are also grateful to the anonymous referees.

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