Sabicea crystallina (N. Hallé) Zemagho, O. Lachenaud & Sonké

Zemagho, Lise A., Liede-Schumann, Sigrid, Lachenaud, Olivier, Dessein, Steven & Sonke, Bonaventure, 2017, Taxonomic revision of Sabicea subgenus Anisophyllae (Ixoroideae, Rubiaceae) from Tropical Africa, with four new species, Phytotaxa 293 (1), pp. 448-450 : 448-450

6. Sabicea crystallina (N. Hallé) Zemagho, O. Lachenaud & Sonké , comb. & stat. nov.

Pseudosabicea aurifodinae var. crystallina N. Hallé, Adansonia , sér. 2, 11: 316 (1971).

Type :— GABON. Rivière Balakabo , sous-affluent de la haute Noya, 18 km WSW de Méla, Monts de Cristal, 20 January 1968, N. Hallé & J.F. Villiers 5428 (holotype P [P03793466]!) .

Sarmentose woody vine, forming dense tangles; stems up to 2 m long, 2–6 mm thick, glabrous or very sparsely villose, with stiff hairs ca. 1.5 mm long. Leaves opposite, strongly unequal, one of them much reduced; smaller leaves with petioles 0–0.2 cm long and blades 0.4–1 x 0.2–0.7 cm; normal-sized leave with petioles 0.9–3 cm long, glabrous or sparsely villose like the stems; blades elliptic to slightly obovate, 8.5–26 x 3.4–11.4 cm, asymmetrical at base with proximal side obtuse to subcordate and distal side acute to obtuse inserted up to 8 mm higher, papyraceous to coriaceous, strongly discolorous; under side green, glabrous or sparsely villose below, with stiff hairs 1–2 mm long; lower side white to pale buff, densely felted below, with woolly hairs; secondary veins 10–19 on each side of the midrib. Stipules opposite, interpetiolar and connate at base with the petioles forming a sheath 3– 8 mm long, the free part narrowly triangular, 5–23 x 1.2–5 mm, entire, acute at apex, erect to patent, glabrous outside or very sparsely ciliate on the margin, glabrous inside except the base with stiff hairs ca. 1.5 mm long. Inflorescences on older stems below the leaves, or sometimes in the axils of the lowest leaves, 1–2 per node, sessile, glomerulate, 1–1.7 cm in diameter, with 5–15 flowers. Bracts and bracteoles ± hidden between the flowers, not enclosing them; bracts triangular, 1.5–3.5 x 0.7–1.5 mm, acute, glabrous or sparsely felted outside and sometimes villose on the margin, inside densely villose with long stiff hairs in the lower half and glabrous in the

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upper half; bracteoles narrowly triangular, entire or shortly toothed, acute to obtuse at apex, 1.5–6.5 x 0.5–1 mm, with same indumentum as the bracts. Flower buds with apex ovoid and slightly enlarged. Flowers 5-merous, sessile or with short pedicel up to 1 mm; only long-styled flowers seen. Hypanthium glabrous or very sparsely villose with stiff hairs. Calyx with purplish tube and white lobes; tube 0.5–1.3 mm, outside glabrous or sparsely villose, inside glabrous; lobes narrowly elliptic to narrowly triangular, 2.5–5.5 x 0.3–1.2 mm, +/- of the same width throughout or slightly broadened near the apex, acute to rounded, thin and flat (not canaliculate), patent to oblique and divergent from each other, glabrous to pubescent outside (see descriptions of subspecies), glabrous inside; 1–4 minute colleters usually present between every pair of lobes. Corolla entirely white; tube narrow, almost cylindrical, 8–11 x 1–2 mm; lobes triangular, 2–2.5 x 1.2–1.5 mm; corolla tube glabrous outside, lobes either glabrous or villose with stiff hairs ca. 1 mm long; mouth and base of lobes inside densely bearded with white moniliform hairs ca. 1 mm long; tube pubescent in upper part down to the base of the anthers inside, with 5 patches of hairs around the middle of the tube. Stamens included or with anther tips slightly exserted in long-styled flowers, inserted above the upper third of the tube, filaments ca. 1.5 mm long; anthers ca. 1.5 x 0.5 mm. Disk cylindrical, ca. 0.3 mm long, glabrous. Style glabrous, ca. 12 mm long, exserted in long-styled flowers; stigmatic lobes ca. 1 mm long, broadly elliptic and +/- flat. Fruits green (probably not mature), obovoid, ca. 5 x 3.5 mm when dry, subsessile or with a short pedicel to 1.5 mm long. Seeds brown, polygonal ca. 0.5 x 0.3 mm, truncate at apex, the surface with dense faint parallel striations.

Discussion: — Sabicea crystallina resembles S. aurifodinae , and was originally described as a variety of it by Hallé (1971). The differences between them are slight, but the two taxa have a different facies and separate ranges, and we prefer to treat them as separate species. Sabicea sciaphilantha and S. ndjoleensis also belong to the same group; the differences between all four species are shown in Table 3.

Notes:—Only two specimens with open, longistylous flowers are known, one from subsp. crystallina and one from subsp. engongensis .

Hallé (1971: 317) regarded the collection N. Hallé & G. Cours 5945 as probably belonging to this taxon; he had earlier referred it with some doubt to S. batesii ( Hallé 1966: 204) . This specimen, although lacking flowers or fruits, is too pubescent for either species, and seems to represent S. sciaphilantha subsp. hirsuta instead.

Conservation status:— IUCN Red List Category: Near-Threatened [NT]. The extent of occurrence is estimated as 5,259.358 km 2 and the area of occupancy as 40 km 2, respectively within the limits for Vulnerable and Endangered under criteria B1 and B2. The species is known from 9 subpopulations representing 7 locations (sensu IUCN 2012), within the limit for Vulnerable under the conditions B1a and B2a. However, there is no evidence of a decline in either extent of occurrence, area of occupancy, extent or quality of habitat, number of locations or number of individuals. The species occurs in a sparsely populated area, and is adaptable to some degree of habitat degradation due to its preference for open habitats. Five of its subpopulations are situated in national parks (Monte Alén N.P. in Equatorial Guinea, and Monts de Cristal N.P. in Gabon). Nevertheless, in view of its small range, it seems appropriate to treat it as Near-threatened.