Two new species of Raphia (Palmae/Arecaceae) from Cameroon and Gabon

Abstract Raphia (Arecaceae, Calamoideae) is the most diverse genus of African palms with around 20 species. Two new species from Cameroon and Gabon, Raphiagabonica Mogue, Sonké & Couvreur, sp. nov. and Raphiazamiana Mogue, Sonké & Couvreur, sp. nov. are described and illustrated. Their affinities are discussed and the conservation status of each species is assessed. For both species, distribution maps are provided. Raphiagabonica is restricted to two small populations from central Gabon, where it occurs on hillsides on tierra firme soil, and close to small streams. Its preliminary IUCN status is Endangered, being amongst the five most threatened palm species in Africa. Raphiagabonica potentially belongs to the moniliform section. Raphiazamiana is largely distributed from south Cameroon to south Gabon and is very common. It is also a multi-used palm, from which wine, grubs and construction material are extracted and sold. It generally occurs in large stands in a wide range of ecosystems such as swamps, coastal forests on partially inundated sandy soils and inundated savannahs. Its large stature, hard to access habitat (swamps) and abundant presence might have discouraged botanists to collect it until now. Raphiazamiana belongs to the taxonomically complex raphiate section.


Introduction
Raphia (Raphiinae, Calamoideae) is the most species-rich genus of African palms with now 22 species currently recognised to date (Dransfield et al. 2008, Stauffer et al. 2014). In addition, most Raphia species are socio-economically important and widely used across tropical Africa (Tuley and Russell 1966, Balick and Beck 1990, Burkill 1997, Obahiagbon 2009). Despite their importance, the taxonomic understanding of this group remains very limited. This is mainly linked of their massive stature and hardto-access wild populations, often thriving in swampy and inundated areas, rendering botanical collections difficult. Based on the shape of the partial inflorescence, five sections were described by Otedoh (1982). Almost all species are restricted to tropical Africa (Stauffer et al. 2014), with a single species occurring in Madagascar (R. farinifera (Gaertn.) Hylander) and one species (Raphia taedigera (Mart.) Mart.) occurring disjunctly in South and Central America (Dransfield et al. 2008). Most species occur in swampy environments forming large dense populations and only one species is so far known from tierra firme in forests (e.g. R. regalis Becc.). Raphia palms are acaulescent or more commonly with an aerial stem which can be solitary or clustered, bearing conspicuous fibres formed through the disintegration of leaf sheath margins (Otedoh 1982, Dransfield et al. 2008. Their leaves are pinnate and very large, up to 25 m in R. regalis (Hallé 1977, Dransfield et al. 2008, being amongst the longest in the plant kingdom. The species of Raphia are hapaxanthic (they die after flowering), monoecious, with basal female and apical male flowers on the same rachillae. The fruits are covered by imbricate scales typical of the Calamoideae subfamily genera (Dransfield et al. 2008).
The two new species reported here stem from extensive field work in Gabon, Cameroon, Republic of Congo and the Democratic Republic of Congo between September 2015 and February 2018.

Material and methods
Herbarium collections were made following methods described in Dransfield (1986). Measurements were taken from fresh and dry plant material collected in the field. Flowers were described following micro-morphology methods. Raphia collections from important international herbaria were studied (BR, FI, G, K, LBV, P, WAG, YA) (herbarium acronyms according to Thiers 2018) and online repositories (http://plants. jstor.org). The descriptions are based on herbarium specimens, field notes and spirit material when available. Unless otherwise stated, the dimensions mentioned for the various organs refer to dry material and the colours to fresh material. The conservation status was estimated for each species following the criteria and categories of the IUCN Red List version 3.1 (IUCN 2012). These were based on the geographical range estimated from herbarium specimens (Schatz 2002). The extent of occurrence (EOO) and the area of occupancy (AOO) were estimated using the online tool GeoCAT (Bachman et al. 2011). The minimum AOO was estimated based on a user defined grid cell of 2 km 2 . Phytogeographical considerations follow White (1979White ( , 1983White ( , 1993. Diagnosis. Raphia gabonica closely resembles R. gentiliana by its solitary stem with curly fibres and the shape of the partial inflorescences. Raphia gabonica differs from R. gentiliana in being a mainly tierra firme species (vs. a swamp species), the shape of its fruits being globose, deltoid or ovoid (vs. ellipsoid) with 11 or 12 rows of scales (vs. 9-11) and a thick mesocarp measuring >8 mm.
Ecology. Raphia gabonica occurs in lowland rain forests, growing on hill sides on tierra firme and also near streams. Seen occurring together with Sclerosperma mannii H.Wendl. and Elaeis guineensis A.Chev.
Distribution. Lower Guinea subcentre of endemism (White 1979). Raphia gabonica is restricted to the northern part of the Ngounié region in Gabon occurring in very small populations in forests. Altitude 76-228 m (Fig. 3).
Preliminary conservation status. Endangered: EN B2ab(ii): Raphia gabonica is a rare species collected from two close locations in central Gabon (Fig. 3). Its minimal area of occupancy (AOO) is estimated to be 8 km 2 (within the limits for Critically Endangered status under criterion B2). To date, two locations are known within the limits of the Endangered status. Both collections were made recently (2015) along important road axes (e.g. Nationale 1) and in unprotected areas (Fig. 3). For each location, several individuals were seen indicating no immediate threat. However, we project that the ongoing loss of its natural habitat linked to increased human activity will induce an important decline of its EOO and AOO. Raphia gabonica is therefore assigned a preliminary status of EN B2ab(ii), joining the almost 5% of continental African palms under this category (Cosiaux et al. 2018) Uses. No uses have been reported for this species.
Notes. Raphia gabonica appears to belong to the moniliform section of Otedoh (1982) linked to the shape of its partial inflorescences. However, the solitary trunk with curly fibres could also suggest a resemblance to species within the temulentae section (e.g. Raphia hookeri G.Mann & H.Wendl. or R. sese De Wild.).  Diagnosis. Raphia zamiana is morphologically most similar to R. monbuttorum in their clustering habitat and straight fibres covering the trunk. Raphia zamiana differs from R. monbuttorum by the size of its stout and stiff rachillae with apical second order rachillae measuring 1 cm in diameter versus less than 1 cm in R. monbuttorum. The inflorescences of R. zamiana are pendulous even from the early stage of development as opposed to the semi obtuse erect position in R. monbuttorum.
Ecology. Raphia zamiana is an Atlantic central African rain forest species, endemic to lower Guinea. It appears to have a wide ecological amplitude, growing in rain forest swamps on periodically inundated soils, in coastal forests on inundated sandy soils or in open vegetation like savannahs associated with inundated soils (e.g. Lope National Park, Gabon,Figs 3,5C). It is generally abundant forming large dense almost monodominant stands. It has been recorded growing sympatrically with R. hookeri and S. mannii.
Distribution. Lower Guinea subcentre of endemism (White 1979). Raphia zamiana occurs in southern Cameroon (Central and South regions) and western Gabon. It is probably also common in Equatorial Guinea although no collections have been made yet. Altitude: 0-700 m (Fig. 3).
Preliminary conservation status. Least Concern. The extent of occurrence of Raphia zamiana is estimated to be 128,243,063 km 2 (far exceeding the 20,000 km 2 upper limit for Vulnerable status under criterion B1) and the area of occupancy is estimated to be 36,000 km 2 (far exceeding the 2,000 km 2 upper limit for Vulnerable status under criterion B2). Moreover, this species is known from 9 locations, the upper limit for sub criterion a-of criterion B2 for the Vulnerable status. However, Raphia zamiana is a widespread and common species in its area of occurrence. It is very common along road sides and is abundant growing in dense colonies. To date, it has not been collected within a protected area, but populations were seen in Campo National Park (Cameroon). Incredibly, its first collection dates to 2012. Botanists might have confused it with the well-known and widespread species Raphia hookeri (although both species are very different in their morphology). Given that collecting Raphias is a hard task because of their massive stature (Dransfield 1986), it was simply omitted. Populations are affected by road building and the drying of swamps for bridges, but these only impact a small number of individuals. Raphia zamiana is therefore assigned a preliminary status of LC, joining most continental African palm species (Cosiaux et al. 2018).
Etymology. The name of this species is derived from its vernacular name in Beti (south Cameroon, north Gabon): Zam.
Uses. This palm is massive thus providing large amounts of thatching material. Its petiole and rachis commonly referred to as 'bamboo' are used for house construction, beds, chairs, baskets and mats. These are generally sold along the roads in south Cameroon. In Gabon, its fruits are sold in markets. These are boiled and said to cure hypertension and diabetes. Finally, this species is also used for wine tapping and as a source of grubs. Vernacular names. Zam (Beti). Notes. Raphia zamiana belongs to the raphiate section (Otedoh 1982). It closely resembles R. monbuttorum Drude and R. laurentii De Wild. in the morphology of their trunks being clustered and covered with straight fibres. However, it is very distinct by having a pendulous inflorescence bearing stout, stiff and straight rachillae. The inflorescences of R. monbuttorum and R. laurentii usually hang at an obtuse angle especially during the young stages of development, becoming pendulous only when brought down by the weight of fruits. Young, recently developing inflorescences are grey-blue turning green later on.
Raphia zamiana is a very conspicuous palm in southern Cameroon and eastern Gabon, being common along roads and in swamps. In addition, we report several important uses, being one of the most useful Raphias (Mogue, personal observation). However, up to now, it remained uncollected, stressing once again that new species well known to local people have yet to be scientifically discovered and described. A similar situation was recorded for the Vietnamese endemic palm Licuala centralis (Henderson et al. 2008). This palm was well known and used to make local hats, but was only scientifically described in 2008.