Research Article |
Corresponding author: Miguel Angel García ( mgarcia@rjb.csic.es ) Academic editor: Yasen Mutafchiev
© 2018 Miguel Angel García, Daniel L. Nickrent, Ladislav Mucina.
This is an open access article distributed under the terms of the CC0 Public Domain Dedication.
Citation:
García MA, Nickrent DL, Mucina L (2018) Thesium nautimontanum, a new species of Thesiaceae (Santalales) from South Africa. PhytoKeys 109: 41-51. https://doi.org/10.3897/phytokeys.109.28607
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Thesium nautimontanum M.A. García, Nickrent & Mucina, a new species from the Matroosberg Mt. of Western Cape Province of South Africa, is described and illustrated. This species shows several morphological features unusual for the genus including stem sympodial branching, indeterminate spicate inflorescences subtended by numerous bracts and fleshy, non-trichome tissue lining the inside of the corolla lobes. Molecular phylogenetic analyses using nuclear ribosomal internal transcribed spacer sequences place this taxon as sister to all African, Madagascan and South American Thesium species. Given that only two proximal populations are known, this species is of conservation concern.
Capensis, endemic plant, Matroosberg mountain, parasitic plant, Santalaceae
Thesium L. is the most speciose genus in the sandalwood order (Santalales) with over 350 species (
The Fynbos Biome, embedded within the South African Cape Floristic Region, sometimes referred to as a Floristic Kingdom (
This paper describes a new species of Thesium that is exceptional from several perspectives. In terms of morphology, it shows several features that are unique in the genus. From the molecular phylogeny perspective, this species holds a special place in that it is sister to the entire clade of African Thesium (250 species).
The morphology of this new species was studied from herbarium samples collected by J. Šibík and I. Šibíková in October 2007 and Mr. Eugene Pienaar in December of the same year. Material from the herbarium samples was rehydrated and examined with a stereomicroscope. DNA extraction, PCR and sequencing of nuclear internal transcribed spacer of ribosomal DNA (ITS) was conducted as specified in
The ITS sequence from the new species was added to the alignment from
To aid interpretation of the flower description, a generalised Thesium flower longitudinal section is shown in Fig.
The extent of occurrence (EOO) and area of occupancy (AOO) were determined using the Geospatial Conservation Assessment Tool with a default cell width of 2 km (GeoCAT,
Diagramatic longitudinal section through a generalised Thesium flower. The figure was composited from numerous species, hence not all features occur in one species. Nearly all characters shown are variable within the genus. The asterisk (*) indicates the unique fleshy tissue seen lining the corolla lobes in T. nautimontanum.
SOUTH AFRICA. Western Cape Province, Cape Winelands District, Matroosberg, southern slope, 33°23'49.3"S, 19°40'29.5"E, elev. 1016 m; 6 Oct 2007, J. Šibík & I. Šibíková MS463 (holotype: MA-877227).
Squamate, glabrous, perennial herb 30–35 cm tall with erect, terete to ribbed sympodial branches; leaves reduced to triangular, acute scales up to 1.7 mm long, increasing in size and density apically, grading into inflorescence bracts. Inflorescences terminal, oblong, crowded spikes bearing up to 50 bracteate flowers, ending in a group of sterile bracts. Flower ca. 2.0 mm long, greenish outside, whitish inside, with triangular external glands between the corolla lobes, internal surface of lobes bearing thick, irregular, spongy and somewhat papillose tissue. Fruit wall marked with conspicuous, strongly raised reticulations.
Perennial herb, squamate, all parts glabrous; rootstock slender, bearing one or few erect flowering stems 30–35 cm tall with sympodial branching that occurs mostly at the base of inflorescences, branches erect, terete or shallowly ribbed. Leaves all reduced to minute scales, the lower ones 0.5–1.0 × 0.8–1.7 mm, broadly triangular, acute, with darkened tips, erect and more or less appressed to the stem, increasing in size upwards and transitioning into bracts, 1.1–1.9 × 0.8–1.1 mm, ovate-triangular to ovate, acute to acuminate, with entire margins, incurved to naviculate but lacking a marked midrib and bearing in their axils undeveloped buds, progressively more crowded towards the base of the inflorescence, greenish to straw-coloured. Inflorescences terminal (on long and short shoots), oblong, spikes 10.5 × 18.5 mm, bearing (15-)24–50 crowded flowers, ending in a group of about 7–14 sterile bracts. Flowers ca. 2.0 mm long, solitary and sessile in the axil of each bract or with a short (up to 0.8 mm long) pedicel. Flower bracts 1.5–2.2 × 1.0–1.4 mm, similar in shape to the bracts at the base of the inflorescence; bracteoles 2, similar to bracts but smaller. Corolla greenish outside, whitish inside; external glands between the corolla lobes inconspicuous, triangular-ovate, pale orange in colour; hypanthium shallow, 0.2 mm long, internal surface glandular; corolla tube ca. 0.4 mm long; corolla lobes 0.7–0.8 × 0.6–0.7 mm, ovate or ovate-triangular, ± obtuse to slightly hooded and with inflexed tips on fruit, erect, margins entire, lacking hairs inside but with a thick, irregular, fleshy and somewhat papillose tissue. Staminal filaments inserted at junction of hypanthium and corolla tube, very short and inconspicuous, stamen not reaching the corolla lobe sinuses, anthers rounded ca. 0.3 mm in diameter, attached to the corolla tube by a small tuft of hairs. Style very short (ca. 0.1 mm) or lacking, thus stigma sessile, lobes not apparent, reaching the base of the anthers. Placenta twisted, ovules 3. Fruits ca. 3.0 mm long, ovary portion subglobose, 1.5–2.1 × 1.6–2.0 mm, greenish, with slightly marked ribs but reticulations strongly raised, crowned with the 1.0 mm long corolla remnant, pedicel not enlarging into an elaiosome.
Thesium nautimontanum M.A. García, Nickrent & Mucina, sp. nov. A habit of plant showing sympodial branching B flowering shoot showing squamate condition, vegetative bracts grading into floral bracts and terminal spicate inflorescence C flower, lateral view D flower longitudinal section E young fruit subtended by bract and two bracteoles. Drawing by J. L. Castillo.
Thesium nautimontanum from the type herbarium specimen. For dimensions, see Figure
Both collections of this species were made on the Matroosberg Mt. in the Southern Hex River mountain range, Western Cape Province, Cape Winelands District, northwest of the De Doorns settlement.
The holotype collection, from 1016 m elevation, occurred on the southern slopes of the Matroosberg Mt. in the FFs8 South Hex Sandstone Fynbos vegetation according to
The second population was discovered at an elevation of 1920 m, close to the summit of Matroosberg (2249 m). Here Thesium nautimontanum was found in a slight depression supporting a dense restioid-ericoid fynbos wetland (dominated by graminoids of the family Restionaceae and shrubs of Erica L.), surrounded by dry fynbos scrub of the FFs30 Western Altimontane Sandstone Fynbos. The soils here are nutrient-poor and sandy, overlying Table Mountain Sandstone. In contrast to the South Hex Sandstone Fynbos, the altimontane fynbos unit receives higher mean annual rainfall (1380 mm on average), peaking from May to August; frequent fog occurrence (due to summer tradewinds) may carry additional precipitation, mitigating the effect of summer drought at high elevations – a phenomenon common to many Cape Fold Mountains (see
The specimens examined had spikes containing both flowers and maturing fruits and were thus at similar developmental stages. As the lower elevation collection was flowering in October and the higher elevation one in December, one can extrapolate that the flowering time ranges from ca. September to January.
The specific name stems from the Matroosberg Mt. where the species was first discovered. In Afrikaans, “matroos” means “sailor” and “berg” means mountain. As the Code of Botanical Nomenclature suggests, epithets formed from a geographic name should be in adjectival rather than substantive form, “nauta” (sailor) and “mons” (mountain) become autimontanum.
According to the World Database of Key Biodiversity Areas (http://www.keybiodiversityareas.org/home), the Hex River Mountains are surrounded by globally and regionally significant areas (UNESCO World Heritage Site ‘Cape Floral Region’), but are themselves not currently included. Due to rugged terrain, nutrient-poor soils not viable for large-scale agricultural activities and relative low-key tourism interest (more of importance on the northern flank of the Matroosberg Mt.), the biota of the Hex River Mts. is not under direct, unmitigated threat. However, fynbos scrub is a naturally fire-prone ecosystem, yet too frequent (or too hot) fires might have negative impacts on the natural post-fire regeneration (e.g.
A section of the Hex River Mts. is under management of CapeNature (the Western Cape provincial nature conservancy authority) and is formally protected in Bokkeriviere Nature Reserve. The coordinates of E. Pienaar M1249 are at 1920 m a.s.l., which place this higher elevation population just south of the boundary of the Reserve. This may well indicate that the species might also occur within the boundaries of the Reserve.
The limited geographic distribution of Thesium nautimontanum is, however, of concern. Using GeoCAT for the two populations, the extent of occurrence was 0.0 and the area of occupancy was estimated at 8.0 km2 which translates to an IUCN Red List category of Critically Endangered, criteria B2 (
Further exploration of these regions should be conducted to determine whether additional populations exist. Even if more populations are encountered, most likely it will stay in the category of Critically Endangered because it is an endemic species restricted to the Matroosberg Mt.
SOUTH AFRICA. Western Cape Province, Cape Winelands District, Matroosberg, southern slope, 33°23'43.48"S, 19°40'19.46"E, alt. 1920 m, 7 Dec 2007, E. Pienaar M1249 (MA-877228, NBG).
The molecular phylogenetic analyses of the ITS data using the three inference methods (ML, MP and BI) produced results generally comparable to those reported in
Phylogram for Thesiaceae that includes Thesium nautimontanum sp. nov. (bold). Values at the nodes indicate maximum likelihood bootstrap, maximum parsimony bootstrap and Bayesian posterior probabilities. The scale bar represents number of substitutions per site. Branch lengths are proportional to the amount of substitutional change, except for the branch connecting the outgroup to the ingroup (here shorted for graphical purposes). Group (clade) names are from
As far as known, Thesium nautimontanum is restricted to the Matroosberg Mt., the highest mountain of the Hex River mountain range. This geomorphologically diverse landscape supports many local and regional endemic plants (see descriptions of the relevant vegetation types in
The present molecular phylogenetic analyses are in agreement with another study with greater taxon sampling (390 accessions representing over 200 taxa) that is currently being prepared for publication (D. Nickrent et al., in prep.). Interestingly, using chloroplast spacer sequences, this species is sister to most African Thesium, however, the equivalent basalmost position is occupied by two clades, one containing Thesium spinosum L.f. and T. spinulosum A. DC. and the next one composed of seven species that often bear simple or compound dichasial inflorescences that mostly occur in the South African Karoo. Incongruences between the nuclear and chloroplast gene trees are currently being investigated and preliminary data indicate chloroplast capture may be occurring, thus obscuring species relationships when using the plastid data.
We are grateful to J. L. Castillo for preparing the illustration of Thesium nautimontanum. Thanks go to Roy Gereau who helped with the Latin construction of the scientific name and to Marcos Caraballo and Romina Vidal-Russell for useful comments on an earlier version of the manuscript. The authors acknowledge contribution of J. Šibík, I. Šibíková and E. Pienaar who made fortuitous collections during field work pursuing their vegetation-descriptive studies. This work was partially supported by grant CGL2006-00300/BOS from the Consejo Superior de Investigaciones Científicas, Real Jardín Botánico (Madrid) to MAG.