Sabicea ezangae Zemagho, O. Lachenaud & Sonké, 2018

Zemagho, Lise, Lachenaud, Olivier & Sonké, Bonaventure, 2018, Four new species of Sabicea (Rubiaceae) from tropical Africa, with additional notes on the genus, Candollea 73 (2), pp. 277-293 : 282-284

Sabicea ezangae Zemagho, O. Lachenaud & Sonké , spec. nova ( Fig. 1D–F , 5 ).

Holotypus: GABON. Moyen-Ogooué: Concession Maurel & Prom , près du Lac Ezanga , 1°05'41"S 10°15'25"E 22.XI.2013, fl., Lachenaud et al. 1544 ( BR [ BR0000024387149 ]!; isotype: BRLU!, LBV!, MO!, P!, WAG!).

Inflorescentiis capitatis, axillaribus et involucratis bracteis 4‒8 liberis cinctis bracteolisque carentibus, calyce tubo brevissimo lobisque anguste ovatis, corollae tubo longiore (16‒ 18 mm) Sabicea calycinae Benth. et S. schaeferi Wernham affinis , sed differt a primo calyce (4‒)5‒ nec 3(‒4)-lobato, et a secundo capitulis 4‒5 floris (nec 7‒15-floris) pedunculo hirsuto (nec appresse-pubescente). Ab ambabus bracteis et calyce hirsutis (nec glabrescentibus), ovario dense villoso (nec glabro vel sparse appresse-pubescente), foliisque subtus indumento mixto pilis longis erectis et brevibus lanuginosis distinguitur.

Twining or creeping liana, up to 3 m tall; young stems cylindrical, 1‒2 mm thick, with a mixed indumentum of soft patent hairs 1.5‒2.5 mm long and much shorter crispate hairs; older stems with scaling bark. Stipules interpetiolar, ovate, 5.5‒10 × 3.5‒6.5 mm, acute at apex, recurved, villose outside, glabrous inside except at the base, persistent. Leaves opposite and equal; petiole 0.4‒2 cm long, with same indumentum as the stems; leaf-blade elliptic, 6‒14 × 2.8‒5.7 cm, rounded at base, acuminate at apex, thinly papyraceous, green on both sides but markedly paler below, drying olive green to olive brown; upper surface sparsely villose with suberect hairs c. 1 mm long, intermixed with shorter uncinate hairs; lower surface with mixed indumentum of rather sparse short woolly hairs, and long soft hairs 1.5‒ 2 mm long (these mostly on the veins); secondary veins 10‒17 pairs, markedly curved and ascending, eucamptodromous; tertiary veins densely reticulate below, but mostly hidden by the indumentum. Inflorescences axillary, solitary, capitate and involucrate, 4 ‒ 5-flowered; peduncle 0.7 ‒6.2 cm long, with same indumentum as the stems; bracts 2‒4 pairs, pale green or sometimes pink-tinged, broadly ovate, 11‒17 × 7.5‒13 mm, free, acute at apex, outside with mixed indumentum of soft erect hairs 1‒1.5 mm long and short crisped hairs, inside sparsely hirsute in the upper half; bracteoles absent. Flowers (4‒)5-merous, sessile. Calyx pale pinkish; tube very short, c. 0.5 mm long, sparsely hirsute outside, glabrous inside; lobes narrowly ovate to lanceolate, 4.5‒9.5 × 1.5‒3 mm, acute at apex, unequal, erect at anthesis, sparsely villose outside and in the upper half inside, alternating with minute colleters. Corolla white; tube 16‒18 mm long × c. 1 mm wide at base and c. 3 mm at apex, very narrowly infundibuliform, outside sparsely silky-pubescent in the upper half, inside sparsely villose in the upper 2/3rds and with short white hairs c. 0.3 mm long in the throat; lobes triangular, 1.5‒2 × 1.5‒2 mm, reflexed, outside densely silky-pubescent, inside minutely papillose. Stamens half-exserted, inserted just under the apex of the corolla tube, subsessile; anthers white, c. 2 × 0.5 mm. Ovary c. 1.5 mm long, 5-locular, densely villose with stiff hairs c. 1.5 mm long. Disk cylindrical, c. 0.7 mm long, glabrous. Style 5-lobed, included, c. 14 mm long including the c. 2.5 mm long linear stigmas, the latter papillose, otherwise glabrous. Fruits and seeds unknown.

Etymology. – Named after Lake Ezanga, in the vicinity of which the species was found.

Distribution, ecology and phenology. – Lower Guinea subcentre of endemism (WHITE, 1979). Only known from the type locality in west-central Gabon ( Fig. 4 ), near Lake Ezanga (about 50 km south-east of Lambaréné), where a dense population of the species was found growing on a forest edge along a track, not far from a savanna boundary, c. 70 m in altitude. The species has never been recollected, although special attention was given to Sabicea spp. during recent botanical inventories in Gabon. Sabicea ezangae is flowering in November.

Conservation status. – Sabicea ezangae is endemic to westcentral Gabon, and has been collected only once. Its extent of occurence (EOO) is therefore not calculable, and its area of occupancy (AOO) is estimated to be 4 km ², within the limit for Critically Endangered status under criterion B2. Its only location is situated in an oil concession, where a dense population occurs on a forest edge along a track. In view of its habitat, the species is likely to be favoured by a limited level of forest clearance, and there is no evidence of a decline. However, any degradation on a larger scale, e.g. for the building of roads or other infrastructures, may affect negatively the extent of quality of habitat, number of locations, number of individuals, and thus AOO and EOO, and the species qualifies for “Critically Endangered” [CR B2ab(i,ii,iii,iv,v)] using the IUCN Red List Categories and Criteria ( IUCN, 2012). It is possible that further populations will be found in the future, but so far this has not happened despite specific prospecting efforts. Given its rarity, and the fact that Sabicea species are generally easy to cultivate, an ex situ conservation program for S. ezangae may be recommended.

Notes. – Sabicea ezangae resembles both S. schaeferi Wernham and S. calycina Benth. ; all three species share capitate inflorescences borne on young stems, with two or more pairs of free involucral bracts, and without bracteoles surrounding the individual flowers; a calyx divided almost to the base in relatively broad lobes; and a relatively long corolla tube for the genus. Their main diagnostic characters are summarised in Table 2 . The differences between S. ezangae and S. schaeferi are rather slight, but taking into account their different ecology, it seems appropriate to treat them as separate species. It is not known if there are additional differences in the fruits, since those of S. ezangae have not been collected, and those of S. schaeferi are known in the very young stage only.

There is also some resemblance between S. ezangae and S. gracilis Wernham , but the latter has a much shorter corolla tube (c. 8 mm long vs 16 mm), calyx lobes and bracts glabrous inside and usually smaller, more strongly discolorous leaves with a dense felt of whitish hairs beneath, and a widely separate range, being restricted to south Cameroon and Equatorial Guinea ( Rio Muni).

It is not known whether this species is heterostylous; only short-styled flowers are known so far.

Figures

Fig. 1. – A. Sabicea desseinii Zemagho, O. Lachenaud & Sonké: inflorescence; B. Sabicea desseinii: immature fruits; C. Sabicea desseinii: mature fruits; D. Sabicea ezangae Zemagho, O. Lachenaud & Sonké: flowering stem; E. Sabicea ezangae: detail of lower leaf surface; F. Sabicea ezangae: inflorescence. [A–B: Texier et al. 1895; C: Sonké & Simo 5004; D–F: Lachenaud et al. 1544] [Photos: A–B: N. Texier; C: B. Sonké; D-F: O. Lachenaud]

Fig. 5. – Sabicea ezangae Zemagho, O. Lachenaud & Sonké. A. Flowering stem; B. Detail of lower leaf surface; C. Node and stipules; D. Inflorescence; E. Flower; F. Flower, longitudinal section. [Lachenaud et al. 1544, BR & BRLU] [Drawing: A. Fernandez]

Fig. 4. – Geographic distribution of Sabicea desseinii Zemagho, O. Lachenaud & Sonké (circles), S. ezangae Zemagho, O. Lachenaud & Sonké (squares), S. jongkindii Zemagho, O. Lachenaud & Sonké (triangles) and S. uniflora Zemagho, O. Lachenaud & Sonké (pentagon).