Sabicea tersifolia (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

15. Sabicea tersifolia (N. Hallé) Zemagho, O. Lachenaud & Sonké , comb. & stat. nov. ( Fig. 32 )

Pseudosabicea arborea var. tersifolia N. Hallé (1964: 398) .

Type:— DR CONGO. En aval de Yanonghe, 9 March 1940, Germain 249 (holotype BR [ BR0000008852038 ]!; isotypes, BR [ BR0000008852090 ]!, EA [EA000001619], K [K000414632]!, P [P00539396]!) .

Shrub or woody vine, probably sarmentose; stems up to 2 m long, 2–6 mm thick, densely white-felted in the young stage, later glabrescent. Leaves opposite, moderately unequal; smaller leaves with petioles 0.3–0.6 cm long and blades 3.5–8.5 x 2.2–4.3 cm; normal-sized laves with petioles 0.6–1.5 cm long, densely white-felted; blades elliptic, 8–17 x 4–8.2 cm, +/- symmetrical, obtuse or acute at base, acute or acuminate at apex, coriaceous and strongly discolorous; upper side green, glabrous or with very sparse woolly hairs in the young stage above; lower side whitish, densely felted with woolly hairs below; secondary veins 8–18 on each side of midrib. Stipules opposite, free and interpetiolar, ovate, 6 x 5–6 mm, entire, acute at apex, erect, glabrescent outside, glabrous inside except the base with silky hairs ca. 2 mm long. Inflorescences axillary on leafy portions of stems, 1–2 per node, sessile, densely glomerulate, 0.7–1 cm in diameter, few-flowered. Bracts and bracteoles very small and hidden between the flowers; bracts elliptic, shortly dentate, shortly connate at base, 3–4 x 1–2.5 mm, densely felted outside, glabrous inside except the base with long silky hairs; bracteoles narrowly elliptic and irregularly dentate, ca. 2 x 1 mm, with same indumentum as the bracts. Flower buds nearly cylindrical, slightly enlarged at apex. Flowers 5-merous, sessile; only short-styled flowers seen. Hypanthium densely white-felted. Calyx tube ca. 1 mm, densely white-felted outside, glabrous inside; lobes triangular, patent and acute at apex, 1–1.5 mm long, densely white-felted outside, glabrous inside; one minute colleter between each pair of calyx lobes. Corolla white; tube narrow, cylindrical, 10–13 x 1.2–2 mm, +/- curved at base; lobes triangular, 2–3 x 1.2–2 mm; corolla densely white-felted except the very base of the tube outside; mouth, base of lobes and distal 2/3 of tube with sparse hairs 0.25–0.5 mm long inside. Stamens included, anthers subsessile, ca. 2 x 0.4 mm, with their apex just reaching mouth in short-styled flowers. Style glabrous, ca. 4 mm long, included in short-styled flowers; stigmatic lobes ca. 1 mm long, narrowly cylindrical. Fruits red, subglobose to ellipsoid, ca. 6 x 6 mm when fresh, ca. 4 x 3.5 mm when dry, densely white-felted in the young stage, sessile. Seeds numerous, brown, polygonal, ca. 0.7 x 0.7 mm, reticulate.

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ZEMAGHO ET AL.

Distribution: — Congolian Domain. Endemic to DR Congo, occuring from the Yangambi region east to the foothills of the Congo-Nile dorsal ( Fig. 31 ); apparently a rare species, collected only three times.

Habitat and ecology: —A heliophilous species growing along rivers and on grassland/forest margins, at 470– 1270 m altitude.

Phenology: —Flowers in March and July; immature fruits in March and mature in August.

TAXONOMIC REVISION OF SABICEA SUBGENUS ANISOPHYLLAE

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Discussion: — Sabicea tersifolia is similar to S. arborea , and was originally described as a variety of it ( Hallé, 1964); however, it shows enough differences (see Table 2) to be recognised as a separate species. It also has a different ecology from S. arborea , being found at lower altitudes.

The habit of the species needs further field studies; two collections are recorded as “lianas” (Germain 249 and Lebrun 5674) and one as a shrub (Lotter 1486). The two flowering collections (Germain 249 and Lebrun 5674) are both of the brevistylous form; the species is likely to be heterostylous, as most species in the genus.

Conservation status:—IUCN Red List Category: Endangered [EN B2ab(i,ii,iii,iv)]. The species is known from three locations, two of which could be georeferenced (the third, “Urega”, being too imprecise). The extent of occurrence is therefore not calculable, while the area of occupancy is estimated as 8 km 2, within the limit for Critically Endangered under criterion B2. None of the localities are protected, and deforestation for agriculture and for mining in the eastern part of its range, represents a clear threat to the species. A decline in the area of occupancy, extent and quality of habitat, number of locations (sensu IUCN 2012) and number of individuals can therefore be projected, and the species qualifies for Endangered status under the conditions B2ab(ii,iii,iv,v).

Additional specimens examined:— DR Congo. South Kivu Province , 2°55.040’S – 28°29.870’E, 18 August 2008, Lotter 1486 ( BR); Urega (Maniema), July 1932, Lebrun 5674 ( BR, P) .

Figures

FIGURE 31. Distribution of Sabicea sthenula and S. tersifolia.

FIGURE 32. Sabicea tersifolia. A, flowering stem; B, flower bud; C, short-styled flower (calyx and ovary removed); D, section of short-styled flower (calyx and ovary removed); E, style; F, immature fruit. All details from Germain 249. Drawing by Antonio Fernandez.