Sabicea sciaphilantha Zemagho, O. Lachenaud & Sonké, 2017

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

13. Sabicea sciaphilantha Zemagho, O. Lachenaud & Sonké , sp. nov.

Type :— GABON. Mabounié, 11 October 2012, B. Sonké & D. Ikabanga 5957 (holotype MO!; isotypes BR!, BRLU!, LBV!, WAG!) .

Sabicea sciaphilantha is similar to S. aurifodinae , S. crystallina and S. ndjoleensis in the sarmentose habit, leaves in very unequal pairs, stipules entire, corolla tube long, and inflorescences borne on the older portion of the stems, usually below the leafy nodes. It differs from the two former species in the dark purple, rather thick and markedly canaliculate calyx lobes bearing stiff hairs inside (vs. calyx lobes white, thin, flat or nearly so, glabrous or with appressed hairs inside). From S. ndjoleensis it can be distinguished by its stipules with free part 10–24 mm long (vs. 5–8 mm long), calyx tube 0.7–1.2 mm long (vs. 1.5–4 mm long), and calyx lobes glabrous outside and stiffly villose inside (vs. densely felted outside and glabrous or appressed-pubescent inside).

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ZEMAGHO ET AL.

Scrambling lianescent shrub; stems 0.4–1.5 m long, 2–5 mm thick, ± arcuate, trailing and rooting at base, usually with short woolly and long stiff hairs intermingled, rarely glabrous. Leaves opposite, strongly unequal, one of them much smaller; smaller leaves subsessile, 0.7–4 x 0.3–2.4 cm; normal-sized leaves with petioles 0.6–2.4 cm long, glabrous or with same indumentum as the stems; blades elliptic to obovate, (8.5) 10–36 x 2.7–11.4 cm, ± asymmetrical at base with proximal side cordate to rounded (rarely cuneate) and distal side rounded to cuneate inserted up to 3 mm higher, acuminate at apex, papery to slightly coriaceous, strongly discolorous; upper side green, glabrous or villose on the midrib (rarely also on the lamina in subsp. hirsuta ) above, with stiff hairs ca. 3 mm long; lower side buff or pinkish-grey, densely felted with woolly hairs and sometimes villose on the midrib below; secondary veins 13–30 on each side of the midrib. Stipules opposite, interpetiolar and connate at base with the petioles into a sheath 3–6 mm long, the free part narrowly triangular to elliptic, 10–24 x 2.5–6.5 mm, entire, acute at apex, erect to patent, glabrous or sparsely felted near the base outside, glabrous except the base with long silky hairs inside. Inflorescences on older portion of the stems, below the leafy nodes, or rarely in the axils of the lower leaves, 1–2 per node, sessile, densely glomerulate, (0.5–) 1–2 cm in diameter, usually many-flowered, exceptionally 1-flowered. Bracts and bracteoles numerous and not clearly distinct from each other, dark purple, ± hidden between the flowers and not enclosing them, narrowly triangular, acute at apex, 2–3 x 0.5–1 mm, glabrous or sparsely villose outside, densely villose inside with long silky hairs all over. Flower buds shortly ovoid and slightly enlarged at apex. Flowers 5-merous, sessile. Hypanthium glabrous to villose with stiff appressed hairs ca. 2 mm long. Calyx dark purple; tube 0.7–1.2 mm, glabrous to densely villose outside, glabrous inside; lobes linear to narrowly triangular, 2–4.5 x 0.2–0.5 mm, acute, rather thick and markedly canaliculate, erect to oblique and ± bending outwards at apex, glabrous outside, densely villose with stiff erect hairs on the margin and inside; 1–2 minute colleters between every pair of lobes. Corolla white; tube narrow and cylindrical, 7–10 x 1–2 mm; lobes triangular, 1.5–3 mm long; corolla glabrous to densely villose with stiff hairs on the lobes and distal portion of tube (base always glabrous) outside; mouth and base of lobes densely bearded inside, with white moniliform hairs ca. 1 mm long; tube either villose from the mouth down to the base of the anthers and with 5 patches of hairs ca. 1 mm lower inside of in long-styled flowers, or glabrous at the distal portion and with a ring of hairs around mid-height in short-styled flowers. Stamens included, filaments ca. 0.7 mm long inserted 3.5 mm below the mouth in long-styled flowers, anthers exserted for most of their length, subsessile inserted near the mouth in short-styled flowers; anthers 1.5–1.8 x 0.5 mm long. Disk cylindrical, ca. 0.3 mm high, glabrous. Style glabrous, 11–11.5 mm long, exserted in long-styled flowers, 7.5 mm long, included in short-styled flowers; stigmatic lobes 2–2.5 mm long, obovate, ± flat. Fruits burgundy red, ovoid, ca. 7 x 6 mm when dry, glabrous or sparsely villose, sessile. Seeds pale brown, polygonal, ca. 0.5 x 0.3 mm, the surface with dense faint parallel striations.

Etymology:— The specific name, sciaphilantha , literally means “shade-loving flower”, in allusion to the fact that the flowers are usually borne in the shade, near the base of the plant, while the leaves are exposed to the light.

Discussion:— Sabicea sciaphilantha closely resembles S. ndjoleensis , S. aurifodinae and S. crystallina ; the differences between them are given in the diagnosis and in Table 3.

Part of the material cited under Pseudosabicea aurifodinae in the Checklist of Gabonese Vascular Plants ( Sosef et al. 2006) actually belongs to Sabicea sciaphilantha subsp. hirsuta (F.J. Breteler 14850, F. Hallé 4537) and subsp. sciaphilantha (D.W. Thomas 6460).

Issembé 259 (WAG) from Mboumi, south of Ndjolé in Gabon, much resembles S. sciaphilantha subsp. hirsuta in general habit and indumentum, but has larger bracts reminiscent of S. ndjoleensis (though slightly smaller). It differs from both species in the calyx lobes broadly elliptic, +/- flat, glabrous outside apart from woolly hairs on the margin. More collections from the same area are needed to decide its status.

Conservation status:— IUCN Red List Category: Vulnerable [VU B2ab(i,ii,iii,iv,v)]. The extent of occurrence is estimated as 51,744.709 km 2 and the area of occupancy as 72 km 2, the latter value being within the limit for Endangered under criterion B2. The species is known from 16 subpopulations representing 7 locations (sensu IUCN 2012), including three protected areas (Lopé National Park in Gabon, Altos de Nsork National Park in Equatorial Guinea, and the Dimonika Biosphere Reserve in Congo). One of the locations at least (Mabounié, in Gabon) is potentially at risk from a mining project. A decline in the extent of occurrence, area of occupancy, extent and quality of habitat, number of locations and number of individuals can therefore be expected, and the species qualifies for Vulnerable status under the conditions B2ab (i,ii,iii,iv,v).

TAXONOMIC REVISION OF SABICEA SUBGENUS ANISOPHYLLAE

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