Sabicea mabouniensis O. Lachenaud & Zemagho, 2015

Lachenaud, Olivier & Zemagho, Lise, 2015, Two new anisophyllous species of Sabicea Aubl. (Rubiaceae) from Gabon, Candollea 70 (2), pp. 219-229 : 224-225

Sabicea mabouniensis O. Lachenaud & Zemagho , spec. nova

( Fig. 1 E-H, 5 ).

Typus: GABON. Moyen-Ogooué: Mabounié , piste du nord-est, 0°43’00’’S 10°35’53’’E, 17.XI.2013, Lachenaud, Stévart, Ikabanga, Issembé, Boupoya & Kaparidi 1446 (holo-: BR!; iso-: BRLU!, LBV!, MO!, P!, WAG !).

Habitu reptante, foliis valde anisophyllis, ovarioque biloculare Sabicea golgothae O. Lachenaud & Zemagho , S. medusula K. Schum. ex Wernham , S. mildbraedii Wernham et S. sthenula (N. Hallé) Razafim. et al. similis est; sed a primo differt foliis basi cordatis indumento subtus laxiore, pedunculis longioribus (0.8-2 nec 0.2-0.5 cm), calyce viride (nec rubro), corolla lobis intus ochraceo-luteis et fauce breviore barbata; ab alteris speciebus inflorescentiis pedunculatis, foliis indumento subtus laxiore et lamina non obscurante, corollaeque lobis intus ochraceo-luteis (nec albis) conspicue distinguitur.

Low creeping herb, with stems rooting at base; stems villous with indumentum consisting of 1.5-2 mm long, pinkish, patent hairs, intermingled with much shorter uncinate hairs. Leaves opposite, strongly unequal especially on upper nodes, often appearing alternate at first sight; reduced leaf with petiole 0-1.3 cm and lamina lanceolate to elliptic, 1.1-3.6 × 0.3-2.6 cm; normal leaf with petiole 2-4 cm long, with similar indumentum to the twigs, and lamina 7-13.2 × 4.2-7.3 cm, elliptic, subcordate and asymmetrical at base, acuminate at apex, papery and slightly discolorous; upper side green, with appressed stiff hairs very sparse on the lamina and denser on the nerves, where they are intermingled with shorter crisped hairs; lower side pale green, with short and rather sparse pinkish-white woolly hairs, intermingled with longer hairs on the nerves; nerves slightly bullate above, pinkish beneath, the laterals 9-12, ascending and almost reaching the margin; tertiary veins densely reticulate and slightly contrasting below. Stipules pinkish-green, 2 per node, interpetiolar, erect, A12-18 × 6-9 mm, broadly ovate and slightly falcate, acute, entire or shortly bidentate, faintly veined, sparsely hairy outside with appressed hairs c. 1 mm long, glabrous inside. Inflorescences axillary, usually in opposite pairs but sometimes only one developing per node, in dense contracted cymes (often appearing falsely umbellate), 1.8-4 cm long; peduncle 0.8-2 cm long, with similar indumentum to the twigs; flowering part 1-2 × 1.4-2.7 cm; ramifications short, <0.4(-1) cm. Bracts pale green, numerous, decreasing in size from the base to the apex of the inflorescence, not clearly forming an involucre, free or shortly connate at base for c. 1.5 mm, entire, rather densely appressed-hairy outside and sparsely so inside; lower bracts broadly ovate, acute, 10-13 × 3-6 mm; upper bracts narrowly lanceolate, c. 8 × 1.2 mm, resembling the calyx lobes. Flowers 5-merous, pedicels 1-2 mm long, densely hairy. Calyx pale green (the apex of lobes often pinkish), with tube very short, c. 0.5 mm; lobes acute, narrowly lanceolate, +/- patent at anthesis, 5-6 × 0.6 mm, densely hairy outside and sparsely so inside, alternating with short colleters at their base. Corolla with white, narrow and almost cylindrical tube, 6 × 1-1.5 mm; lobes pale ochre-yellow inside, triangular, patent, 1.3-1.7 mm long; outside of corolla with short, c. 0.5 mm long appressed hairs on lobes and upper 1/5th of tube, otherwise glabrous; inside of corolla sparsely hairy in upper half of tube and more densely so around the throat, with rather short moniliform hairs c. 0.5 mm long. Stamens included with apex almost reaching throat; anthers sessile, 1.3 × 0.5 mm, shortly apiculate. Ovary c. 2 mm long, densely appressed-hairy, 2-locular. Disk shortly cylindrical, c. 0.3 mm, glabrous. Style bifid, included, reaching about the mid-height of anthers, glabrous, 5 mm long including the 1.5 mm long stigmas, these dorsally compressed and rounded at apex. Fruits unknown.

Distribution and ecology. – Sabicea mabouniensis is known from a single site in the Mabounié area, in West-Central Gabon ( Fig. 4 ). It is apparently a very rare species: although the area has been relatively well-prospected in recent years, no other sites were found. The species grows on a sunny forest edge along a track, a common habitat for species of the genus. It occurs there alongside another new species of Sabicea (Lachenaud et al. 1447) ; the latter is not strictly endemic to the region, and will be described elsewhere.

Conservation status. – The new species is known from a single subpopulation, representing a single location, and occurs in a mining concession. The AOO of S. mabouniensis is estimated at 4 km ², within the threshold for Critically Endangered status under Criterion B2 (the EOO is not calculable). It is thus extremely susceptible to any threat, the most important of which is deforestation for mining. Although the area where it occurs is not to be immediately affected by the mining project, we anticipate that this pressure will increase in the future. A decline in the AOO, extent and quality of habitat, number of subpopulations and number of individuals can therefore be expected, and the species should thus be assigned a preliminary status of “Critically Endangered” [CR B2ab(ii,iii,iv,v)].

Notes. – Sabicea mabouniensis is morphologically very close to S. golgothae , also described in this article (see under that species for more details). It also superficially resembles other low anisophyllous species ( S. medusula , S. mildbraedii and S. sthenula ) but is quite easily separated by the pedunculate inflorescences, the weakly discolorous leaves with hairs not obscuring the under surface (vs. strongly discolorous with a dense felt of woolly hairs obscuring the under surface), and the corolla with short hairs in the throat and lobes ochre-yellow inside (vs. corolla long-bearded in the throat and with the lobes entirely white) ( Table 1 ).

Only short-styled flowers have been observed in S. mabouniensis . Due to the rarity of the material, it is not possible to determine whether the species is heterostylous, as usual in the genus.

Figures

Fig. 1. – Sabicea golgothae O. Lachenaud & Zemagho.A. Habit; B. Underside of leaves; C. Inflorescence; D. Fruits. Sabicea mabouniensis O. Lachenaud & Zemagho. E. Habit;F. Detail of stem with inflorescences; G. Inflorescences; H. Underside of leaf. [A-D: Lachenaud et al. 2116; E-H: Lachenaud et al. 1446] [Photos: A, C, F, H: O. Lachenaud; B, D, E, G: E. Bidault]

Fig. 5. – Sabicea mabouniensis O. Lachenaud & Zemagho. A. Habit; B. Detail of lower leaf surface; C-D. Bracts; E. Node with two stipules, one reduced leaf, one petiole and the base of a peduncle; F-G. Different views of inflorescence; H. Disk and base of calyx, seen from above; I. Flower;J. Longitudinal section of flower; K. Corolla lobe, seen from outside. [Lachenaud et al. 1446, BR & BRLU] [Drawing: Hans de Vries]

Fig. 4. – Distribution of Sabicea golgothae O. Lachenaud & Zemagho (white square) and S. mabouniensis O. Lachenaud & Zemagho (circle).