Ceropegia buraoensis Bruyns, 2020

Bruyns, Peter V., Klak, Cornelia, Mazuch, Tomáš, Gelle, Faysal Jama, Elmi, Hassan Sh Abdirahman & Hanáček, Pavel, 2020, New species of Ceropegia (Apocynaceae) from the Horn of Africa, Phytotaxa 441 (2), pp. 195-202 : 196-197

Ceropegia buraoensis Bruyns , spec. nov.

Type:—SOMALILAND. ± 20 km east of Burao towards Gebo Gabo, 980 m, Oct. 2019, Bruyns 13781 (holotype BOL!, isotype, HARG!). Figs 1 , 2 .

This new species differs from the vegetatively similar C. mijerteina ( Lavranos 1971b: 64) Bruyns in Bruyns et al. (2017: 418) by the campanulate flowers with shallowly bowl-shaped tube that only contains the lower part of the gynostegium.

Small dense to diffuse mat-forming succulent 60–300 mm in diam. Branches prostrate and rooting along entire length, 30–200 × 6–10 mm, dark brown-green to green, papillate and glossy between papillae; tubercles rectangular to slightly hexagonal, slightly fused into 7–8 rounded angles along branch, each tipped by fleshy sagittate papillate ascending leaf-rudiment 1–1.5 mm long with bases extended into 2 rearward-pointing papillate lobules on either side, soon drying out and gradually wearing off. Inflorescences sessile, several near apex of branch, each with (1) 2 flowers opening ± simultaneously (if paired); pedicel 0.5–1 × 0.5 mm, papillate, holding flower facing outwards; sepals 2–3 mm long, ± 0.5 mm broad at base, pale green, papillate, linear, attenuate. Corolla campanulate, 4–5 × 4–6 mm; outside ± shiny maroon, papillate; inside pinkish yellow or orange towards tips becoming redder towards base, smooth and dull, glabrous; tube shallowly bowl-shaped, ± 1 × 3 mm; lobes ascending and spreading towards tips, 3–5 × 2–3 mm, slightly folded longitudinally, acute. Corona ± 2 × 3 mm, ± circular in face view, glabrous, sessile; outer lobes united lower down into bowl slightly exceeding anthers, ± 1.5 mm long, ascending, bifid above into deltate teeth, pale dull translucent yellow becoming greenish towards base, with faint reddish marks inside; inner lobes ± 1.5 mm long, linear, obtuse, adpressed to backs of anthers and rising in short column in centre, without dorsal projection, pale yellow towards bases changing to maroon near tips.

Distribution & Habitat:— Ceropegia buraoensis occurs south of the escarpment in Somaliland, where it was first observed by one of us (TM) between the towns of Burao and Sheikh. After good rains in summer 2019, it was found to be reasonably widespread in the area between Burao, Sheikh and Gebo Goba and also further west between Odwein and Hargeisa. These habitats lie at altitudes between 950 and 1400 m and receive an average of 200–250 mm of rain annually, falling mainly in summer.

Generally, plants grow in reddish loamy sand in flat featureless areas among scattered trees, often flourishing in the protection of the low, spreading shrubs of Cadaba glandulosa Forsskål (1775: 68) . Very occasionally they were also observed on gentle stony slopes, but then they also grew in the protection of larger shrubs.

Discussion:—This new species belongs to sect. Echidnopsis ( Hooker 1871: t. 5930) Bruyns in Bruyns et al. (2017: 416). This is on account of its low, mat-forming habit with 7- to 8-angled, prostrate branches and relatively small flowers produced in small sessile inflorescences near the tips of the branches. Vegetatively it resembles C. mijerteina closely. This is particularly in respect of the prostrate, mostly 8-angled branches rooting along their entire length, with a papillate surface that is somewhat shiny between the papillae and in the similarly-shaped leaf-rudiments (though those of C. mijerteina lack the rearward-pointing lobules found here). The papillae on the branches allow the surface to become covered with sand and dust, adding to the inconspicuousness of the plants during the dry season, a phenomenon also known in C. malum ( Lavranos 1971a: 10) Bruyns in Bruyns et al. (2017: 417). Ceropegia malum also has prostrate branches, but they are 5- to 6-angled and the tubercles are sharply ridged rather than obtuse, giving rise to the continuous, sharper angles along the branches that are typical of this species. Consequently its branches have a different appearance to those of both C. buraoensis and C. mijerteina .

Florally C. buraoensis is very different from both C. malum and C. mijerteina . Although the flowers are small and somewhat campanulate, they only have a very short tube, which just reaches the level of the outer corona, whereas C. mijerteina has pendulous flowers with a long tube (15–25 mm long) and small deltate lobes 1–2.5 mm long around its mouth ( Bruyns 1988: fig. 28). The flowers of C. malum exhibit a particularly peculiar pollination syndrome and have a unique, apple-like shape (± 20 mm in diam.) that is mostly made up of a broad, tubular part, with small, inwardlypointing lobes in the centre of the top of this structure ( Bruyns 1988: fig. 29). In C. buraoensis the flowers usually mature in pairs, which open more or less simultaneously. They are dull reddish yellow inside, somewhat darker than the more yellowish corona. Their corona is also different in shape to that of both C. malum and C. mijerteina , where the outer series is united into an urn-like structure with a narrow mouth and the inner lobes are reduced to short bumps pressed to the bases of the anthers from the inside of this urn-like structure ( Bruyns 1988: fig. 28, 29).

Unpublished analyses of DNA-data, using the same gene-regions as in Bruyns et al. (2014) place C. buraoensis as a strongly supported sister to three Socotran species C. bentii ( Hooker 1901: t. 7760) Bruyns in Bruyns et al. (2017: 418), C. insularis ( Lavranos 1970: 136) Bruyns in Bruyns et al. (2017: 418) and C. socotricola Bruyns in Bruyns et al. (2017: 418). In this group of Socotran species, the flowers vary remarkably in shape from almost rotate to deeply tubular. Clearly the shape of the corolla is very labile among closely related species in sect. Echidnopsis , so that the shape of the corolla in C. buraoensis is not out of place among these. However, the vegetative features mentioned above are not present in any of these Socotran species, where their branches are not prostrate, they are relatively smooth and the leaf-rudiments are much less conspicuous.

Figures

FIGURE 1. A, B, Ceropegia buraoensis. A, branch with flower. The rearward-pointing bases of the leaf-rudiments can clearly be seen here. B, branch showing rear of corolla. C, Ceropegia marronina, Bruyns 13247 (BOL), D, Ceropegia pseudorhynchantha, Bruyns 11584 (BOL, E. MO). Photographs by:A, B, T. Masuch. C, D, P.V. Bruyns.

FIGURE 2. Ceropegia buraoensis. A, side view of flower (scale 2 mm). B, side view of dissected flower (scale 2 mm). C, face view of gynostegium (scale 1 mm, as for D, E). D, side view of leaf-rudiment. E, rear view of leaf-rudiment. F, pollinarium (scale of C 0.25 mm). Drawn from Bruyns 13781 (BOL) by P.V. Bruyns.