Sabicea mapiana 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

8. Sabicea mapiana Zemagho, O. Lachenaud & Sonké , sp. nov. ( Fig. 17 )

Type :— GABON. Mabounié, piste du nord-est, 17 November 2013, O. Lachenaud, T. Stévart, D. Ikabanga, Y. Issembé, A. Boupoya & J. D. Kaparidi 1447 (holotype BR!; isotypes BRLU!, LBV!, MO!, P!, WAG!) .

Sabicea mapiana resembles S. batesii , S. sthenula , and some variants of S. mildbraedii var. glabrescens in the disposition of the leaves, which are solitary at each node and opposed to a stipule. The species differs from S. batesii in the very low and creeping habit (vs. sarmentose), the presence of stiff hairs on the stems, the inflorescences borne inside the stipules (vs. arising through a hole at their base), the calyx lobes 3–4.5 mm long (vs. 1.7–2.5 mm long) and the usually smaller leaves. From S. sthenula , it differs in the entirely white corolla, the usually shorter calyx lobes with dense woolly indumentum outside, and the presence of dense woolly hairs on the stems. From S. mildbraedii var. glabrescens it is separated by the calyx lobes 3–4.5 mm long (vs. 1–1.8 mm long), the presence of long stiff hairs on the ovaries and fruits (vs. densely white-felted, without stiff hairs), the flowers with anthers always included (vs. exserted in short-styled flowers) and the usually lower habit.

Small herb <10 cm tall, forming ground-covering patches; stems creeping or ascending only at the distal nodes (decumbent), densely felted with woolly hairs and sparsely villose, with stiff patent hairs 1.5–3 mm long. Leaves single at each node and opposed to a stipule; petioles 1–4.5 cm long, with same indumentum as the stems; blades elliptic, 5.8–15.5 x 3.2–8 cm, ± asymmetrical at base, proximal side rounded to cordate, distal side acute to subcordate inserted up to 5 mm higher, acuminate, papyraceous to coriaceous, strongly discolorous; upper side dark green, sparsely villose above, lower side with stiff hairs 1–2 mm long; pinkish-white, densely felted with woolly hairs below; 7–13 secondary veins on each side of midrib. Stipules solitary and leaf-opposed, green, narrowly elliptic to broadly ovate, 10–22 x 6–15 mm, multifid, with 5–10 lobes 1.5–4 mm long, erect, sparsely felted to nearly glabrous outside, villose on the margin with stiff hairs ca. 1 mm long, glabrous inside except the base with dense silky hairs ca. 3 mm long. Inflorescences on leafy stems, one per node, opposed to the leaf and ± surrounded by the stipule, sessile, glomerulate, with about 7 flowers. Bract solitary, opposed to the stipule and ± enclosing the inflorescence, spathaceous, 7–10 x 6 mm, concave, acute or shortly 2- to 3-dentate at apex, densely felted outside, villose on margin, glabrous inside except the base with silky hairs ca. 2 mm long; bracteoles narrowly elliptic, 4–11 x 1–3 mm, entire to shortly dentate, with same indumentum as the bracts. Flower buds unknown. Flowers 5-merous, sessile; only short-styled flowers seen. Hypanthium densely villose, with stiff hairs ca. 2 mm long intermingled with short uncinate hairs. Calyx buff outside, green inside; tube 1.5–2 mm long, densely felted outside, glabrous inside; lobes narrowly triangular, 3–4.5 x 0.6–1.3 mm, acute at apex, canaliculate inside, erect to patent, densely felted outside, villose with stiff hairs on the margin, sparsely villose with short appressed hairs in the central area inside; one minute colleter between every pair of lobes. Corolla white; tube narrowly funnel-shaped, 6 x 1–2 mm; lobes triangular, 2–2.5 x 1–1.3 mm; outside of corolla tube glabrous or sparsely villose in upper part, the lobes densely pubescent with stiff hairs ca. 1 mm long intermingled with a shorter dense felt of woolly hairs; mouth and base of lobes inside densely bearded with white moniliform hairs 1–1.5 mm long; tube villose in the upper 1.5 mm down to the base of the anthers inside, and with a separate ring of hairs slightly above mid-height inside. Stamens included in short-styled flowers, with filaments ca. 1 mm long, inserted slightly above the median portion of corolla tube, anther tips almost reaching the mouth; anthers 1.2–1.5 x 0.6 mm. Disk cylindrical, ca. 0.3 mm long, glabrous. Style glabrous, 4.5–5 mm long, included in short-styled flowers; stigmatic lobes 1–1.5 mm long, elliptic and slightly compressed. Fruits green (probably not fully mature), obovoid, 7–9 x 4–7 mm when dry, densely villose, subsessile. Seeds brown, polygonal, ca. 0.6 x 0.4 mm, the surface with dense parallel striations.

Etymology:— The species is named after Dr. Jeannette Mapi-Sonké, for her constant encouragement and advice to the first and last authors of this work.

Distribution: —Lower Guinea Domain. Apparently endemic to southwest Gabon, where only known from the Doudou Mts, and the Mabounié region east of Lambaréné ( Fig. 18 ). Possibly more widespread, but evidently uncommon.

Habitat and ecology: —The species is encountered along forest roads, where it locally forms patches covering the ground. In its type locality it grows alongside the rare endemic species Sabicea mabouniensis O. Lachenaud & Zemagho (2015: 224) .

Phenology: —Flowering in November; fruits (probably immature) in February and May.

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Discussion:— This species resembles S. batesii , S. sthenula , and some variants of S. mildbraedii var. glabrescens in having pseudoalternate leaves opposed to a stipule; the differences between the four species are given in the diagnosis and in Table 4. Only the type collection bears flowers, which are of the brevistylous form. The species is likely to be heterostylous, as usual in the genus.

Conservation status:—IUCN Red List Category: Endangered [EN B1ab(i,ii,iii,iv,v) +B2ab(i,ii,iii,iv,v)]. The extent of occurrence is estimated as 222.656 km 2 and the area of occupancy as 12 km 2, both within the limit for Endangered under the criteria B1 and B2 respectively. The species is known from three subpopulations, representing two locations (sensu IUCN 2012). One of these locations (the Mabounié area, with two subpopulations) is potentially at risk from a mining project. Therefore, a decrease in the extent of occurrence, area of occupancy, extent and quality of the habitat, number of locations and number of individuals can be projected, and the species qualifies for Endangered under the conditions B1ab(i,ii,iii,iv,v) and B2ab(i,ii,iii,iv,v).

Additional specimens examined (Paratypes):— GABON. Foot of Doudou Mountains , 25–35 km W of Mandji, 15 February 2008, S. Dessein, O. Lachenaud, S. Janssens, Y. Issembe & T. Nzabi 1865 ( BR, WAG, MO); Mabounié, forest, E of the mine, 2 May 2012, T. Stévart, C. Nyangala & W. Mbading Mbading 4130 ( MO) .

Figures

FIGURE 17. Sabicea mapiana. A, flowering stem; B, detail of lower side of leaf; C, detail of a node with inflorescence, stipule enclosing it, and base of leaf; D, bract seen from outside; E, bract enclosing a very young inflorescence, seen from inside; F and G, bracteoles (inside); H, bracteole (outside); I, corolla seen from above; J, calyx and ovary; K, section through calyx and ovary (corolla removed); L, section of short-styled flower. All details from Lachenaud et al. 1447. Drawing by Hans De Vries.

FIGURE 18. Distribution of Sabicea mapiana and S. medusula.