Sabicea sthenula (N. Hallé) Razafimandimbison, B. Bremer, Liede & S.A. Khan

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

14. Sabicea sthenula (N. Hallé) Razafimandimbison, B. Bremer, Liede & S.A. Khan (in Khan et al. 2008: 14) ( Fig.

30)

Pseudosabicea sthenula N. Hallé (1966: 208) .

Type :— GABON. Mboundou, SE of Makokou, 27 February 1961, N. Hallé 1339 (holotype P [P00077600]! isotype BR [ BR0000008852045 ]!, K [K000414622]!, P [P00077601]!)

Creeping herb, <10 cm tall; stems closely appressed to the ground or sometimes shortly ascending at apex, 1–1.5 mm thick, villose with patent or slightly reflexed ca. 2 mm long silky purplish hairs, sometimes intermingled with much shorter uncinate hairs. Leaves solitary at each node, or sometimes opposite and very unequal, one of them vestigial; petioles 0.5–8.7 cm long, with indumentum similar to the stems; blades elliptic, 4.2–12 x 2.4–8.5 cm, cordate to obtuse and +/- asymmetrical at base with the distal side inserted 0–4 mm above the proximal side, acute or shortly acuminate at apex, papery, strongly discolorous; upper side green above, sparsely villose with stiff and +/ - appressed hairs ca. 1 mm long, intermingled with short uncinate hairs on veins above; lower side buff to whitish, densely felted with woolly hairs throughout, and villose on the midrib (sometimes also sparsely on the lamina), with stiff hairs ca. 2 mm long below; secondary veins 6–9 on each side of midrib. Stipules solitary and opposed to the leaf of the same node, or rarely opposite if two leaves per node, pale green to reddish, erect, broadly ovate, 8– 15 x 6.5–16 mm, usually divided for 1/3 to 2/3 of their length into 5–14 narrowly triangular segments 1–7 mm long, sometimes entire when two stipules per node, sparsely villose to nearly glabrous outside, villose on the margin, glabrous inside except the base with silky hairs ca. 2 mm long. Inflorescences on leafy stems, one per node, opposed to the leaf and +/- surrounded by the stipule, sessile, densely glomerulate, with 3–10 flowers. Bract solitary, opposed to the stipule and +/- surrounding the inflorescence when young, narrowly ovate, 6–10 x 2.5–3 mm, entire and acute at apex, sparsely villose outside and densely so on the margin, glabrous inside except for long hairs near the base; bracteoles narrowly triangular, entire and acute at apex, 7–9 x 1 mm, with same indumentum as the bracts. Flower buds nearly cylindrical, slightly enlarged at apex. Flowers 5(–6)-merous, sessile, heterostylous. Hypanthium densely villose, with silky hairs ca. 2 mm long. Calyx pale green on both sides; tube 1–1.5 mm long, glabrous or sparsely villose outside, glabrous inside; lobes narrowly triangular, 4–6 x 0.5–1 mm, gradually narrowing to the acute apex, slightly channelled on the inside, erect to patent, villose on the margin with silky hairs ca. 1.5 mm long, glabrescent or sparsely villose outside (sometimes with very sparse woolly hairs present as well), glabrous inside or sparsely villose with appressed silky hairs in the central part; one tiny colleter between each pair of calyx lobes. Corolla with pink tube and white lobes; tube narrow, almost cylindrical, 7–7.5 x 1–1.3 mm; lobes narrowly triangular, 2–3 x 0.8–1.2 mm; corolla villose outside on the lobes and sometimes also on the distal 1/4 th of the tube, with +/- stiff hairs ca. 1 mm long intermingled with short and very sparse woolly hairs, base of tube glabrous outside; mouth densely bearded with white moniliform hairs c. 1 mm long inside; tube sparsely villose from the mouth down to the base of the anthers inside in long-styled flowers, villose from the mouth down to the insertion of the stamens, with a separate ring of short hairs slightly above mid-height inside in short-styled flowers. Stamens always included and subsessile, attached either near the middle of the tube (long-styled flowers) or around the upper 1/5 th of the tube, with their apices almost reaching mouth (short-styled flowers); anthers ca. 1.3 x 0.3 mm. Disk cylindrical, ca. 0.5 mm long, glabrous. Style glabrous, either ca. 8 mm long,slightly exserted but +/- hidden between the hairs of the corolla-mouth in long-styled flowers, ca. 5 mm, included in short-styled flowers; stigmatic lobes 1–1.3 mm long, narrowly elliptic and +/- flattened. Fruits apparently remaining green at maturity, ovoid, 5–9 x 3.5–6 mm when dry, densely villose. Seeds pale brown, narrowly polygonal, ca. 0.8 x 0.3 mm, the surface with dense parallel striations.

Distribution: —Lower Guinea Domain. The species occurs in Cameroon where it is rare, Gabon where it is common and widespread, and western Republic of Congo ( Fig. 31 ).

Habitat and ecology: —Half-shaded places in forest, along forest streams (which are probably the original habitat) and in degraded areas, often covering the ground on shaded roadsides; from near sea level to 830 m in altitude.

Phenology: —Flowers in January–April and October–November; fruits in February–May and October– November.

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Discussion: — Sabicea sthenula resembles S. medusula in the creeping habit, corolla with a pink tube and white lobes, and long and narrow calyx lobes. In the two former characters it also resembles S. parmentierae . The differences between these species are summarised in Table 5 (see also below). S. sthenula also resembles S. mapiana which has a similar low creeping habit and pseudoalternate leaves. The latter species differs in its entirely white corolla, and shorter and markedly discolorous calyx lobes (see Table 4).

Sabicea sthenula usually has leaves solitary at each node, opposed to the stipule of the same node; however, occasional variants with two unequal leaves and two stipules per node have been noted (de Foresta 976, Lejoly 96/ 680, Dessein et al. 2264). These variants are quite similar to S. medusula ; see Key and Table 4 for morphological differences. Sosef et al. 2669 (WAG), from southern Gabon, is probably also one such variant, but the specimen is poor and has the leaves narrower than usual for S. sthenula .

A collection from south Cameroon, J. Raynal & A. Raynal 10184 (P) and two from north-eastern Gabon, Dauby et al. 1746 (BRLU, MO) and A.M. Louis et al. 2563 (BR, WAG) show intermediate characters between S. medusula and S. sthenula . They resemble S. medusula in their short bracts and very narrow calyx lobes with stiff hairs, but have multifid stipules and leaves with 6–9 pairs of lateral veins, as in S. sthenula . Their identity is at present unclear; they may represent a new taxon.

Conservation status:— IUCN Red List Category: Least Concern [LC]. The extent of occurrence is estimated as 258,268.920 km 2, and the area of occupancy as 80.000 km 2, the latter value being within the limit for Endangered under criterion B2. However, the species is known from more than 10 locations (including one protected area, the Dimonika Biosphere Reserve in Congo) (sensu IUCN 2012). Most of its range is sparsely populated, and due to its preference for open habitats, the species benefits from small-scale forest clearance. It is also very likely to be more widespread than records suggest, as it is neglected by collectors due to its low size. It is therefore not threatened at present.

Additional specimens examined:— CAMEROON. Central province: Mefou proposed National Park, M. Cheek, Essama, V. Nana, Njume, Greene, Holding & Bury 11557 (BR, P, WAG). GABON. 5–10 km E of Saint

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Germain, E of Okano River, 19 April 1988, F.J. Breteler, C.C.H. Jongkind & J. Dibata 8821 (BR, LBV, MO, P, WAG); Makande surroundings, about 65 km SSW of Booué, 2 March 1999, F.J. Breteler 15282 (BR, WAG); zone de Mabounié, 45 km SE Lambaréné, 16 November 2013, E. Bidault, E. Akouangou & J.- Y. Serein 1340 (BRLU); Estuaire, savane Boyan – Oyan, 25 January 1997, M.A. Delegne 18-T25 (WAG); foothills of Koumounabouali massive, NE of Bemboudié, 14 February 2008, S. Dessein, O. Lachenaud, S. Janssens, Y. Issembe & T. Nzabi 1829 (BR, K, LBV, MO, WAG); Mouyanama Falls, at base of Mt Songou, 23 February 2008, S. Dessein, O. Lachenaud, S. Janssens, Y. Issembe & T. Nzabi 2112 (BR, LBV, WAG); ca. 50 km on road Lastoursville-Mounana, 1 March 2008, S. Dessein, O. Lachenaud, S. Janssens, Y. Issembe & T. Nzabi 2264 (BR, WAG); Base of Mt Iboundji, path to waterfalls, 03 March 2008, S. Dessein O. Lachenaud, S. Janssens, Y. Issembe & T. Nzabi 2342 (BR, LBV); Mboundou, SE de Makokou, 27 February 1961, N. Hallé 1378 (BR, P); route Mimongo à Mbigou, 22 May 1963, N. Hallé & G. Cours 6160 (P); Mabounié, 18 November 2013, O. Lachenaud, T. Stévart, D. Ikabanga, Y. Issembé, A. Boupoya & J. D. Kaparidi 1468 (BRLU, LBV, MO); Minkébé area, 20 March 1990, Minkébé Series AM 29 (WAG); ibid., 19 March 1990, Minkébé Series W 55 (WAG); ibid., 27 April 1990, Minkébé Series W 163 (WAG); IFL logging concession, along Waka river, 10 November 2009, T. Stévart, D. Nguema, E. Mounoumoulossi, P. Bissiemou & E. Akouangou 3304 (BR); Mabounié, 12 October 2012, B. Sonké & D. Ikabanga 5974 (BR, BRLU); Ogooué-Lolo: Forêt des Abeilles, 11 km WSW of Gongué forestry camp, 13 January 2001, J.J. Wieringa, C.C.H. Jongkind, J.G. Schoonhoven & M. Mbombet 4132 (BR, MO, WAG); upper Waka area, 8 km on a forestry road heading SE from IFL forestry camp, 30 March 2004, J.J. Wieringa, B. Nziengui, J.-M. Moussavou & M. Mbombet 5154 (BR, WAG); 15 km on the road Moukabou to Mbigou, 14 March 2013, J.J. Wieringa, A.S.J. van Proosdij & T. Nzabi 7421 (WAG). REPUBLIC OF CONGO. Dimonika, 30 April 1986, H. de Foresta 976 (P); Grand escarpement d’Odzala, entre le Belvédère et le camp du daman, 24 November 1996, J. Lejoly 96/680 (BR).

Intermediate specimens between S. sthenula and S. medusula :— CAMEROON. Tom , 12 km E Nyabesan, 4 March 1963, J. Raynal & A. Raynal 10184 (P, YA) . GABON. CFAD Rougier Ivindo , Ouest du Parc National de l’Ivindo, zone tampon, 16 March 2009, G. Dauby, D. Nguema, E. Mounoumoulossi & P. Bissiemou 1746 ( BRLU, MO) ; Koumameyong , November 1987, A.M. Louis., F.J. Sterck & A.A.Elias 2563 ( BR, WAG) .

Figures

FIGURE 30. Sabicea sthenula. A, flowering stem; B, stipule, C, inflorescence; D, detail of calyx lobe, inside; E, detail of calyx lobe, outside; F, short-styled flower; G, section of short-styled flower (calyx, ovary and style removed); H, style of short-styled flower; I, detail of the lobes and upper part of corolla tube inside; J, fruit. From N.Hallé 1339 (A), Breteler et al. 8821 (B–C, F–I), Wieringa et al. 4132 (D–E). Drawing by Antonio Fernandez.

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