Sabicea golgothae 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 : 220-224

Sabicea golgothae O. Lachenaud & Zemagho , spec. nova

( Fig. 1 A-D, 2 , 3 ).

Typus: GABON. Moyen-Ogooué: Mabounié , 0°46’31’’S 10°32’30’’E, 2.XI.2014, Lachenaud, Bidault & Lissambou 2116 (holo-: BRLU !; iso-: BR!, G!, LBV!, MO!, P!, WAG !).

Habitu reptante, foliis valde anisophyllis, ovarioque biloculare Sabicea mabouniensi O. Lachenaud & Zemagho , S. medusula K. Schum. ex Wernham , S. mildbraedii Wernham et S. sthenula (N. Hallé) Razafim. et al. similis est. A S. mabouniensi differt foliis basi acutis vel obtusis (nec cordatis) et valde discoloribus indumento subtus lamina obscurante, pedunculis brevioribus (0.2-0.5 nec 0.8-2 cm), calyce rubro (nec viride), corollaque omnino alba fauce longiore barbata; ab alteris speciebus inflorescentiis breviter pedunculatis (nec sessilibus), calyce rubro, fructibusque maioribus distinguitur.

Low creeping herb, 5-15 cm high, with stems rooting at base; stems villous, with indumentum consisting of c. 2 mm long, pinkish, patent hairs, intermingled with much shorter uncinate hairs. Leaves opposite, highly unequal especially on upper nodes, often appearing alternate at first sight; reduced leaf with petiole 0-1 cm and lamina lanceolate to elliptic, 1.2-6.3 × 0.3-2.9 cm; normal leaf with petiole 1.2-3.2(-5.5) cm long, with similar indumentum to the twigs, and lamina (5.8-)8-13.8 × (2.2-) 3.7-6.5 cm, elliptic, acute to obtuse and often asymmetrical at base, acuminate at apex, papery and strongly 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 pinkish-buff, with dense persistent felt of woolly hairs (becoming sparser but still visible on old leaves), intermingled with long stiff appressed hairs on the nerves and on the margin; nerves slightly bullate above, pinkish beneath, the laterals 9-12, ascending and almost reaching the margin; tertiary veins densely reticulate and contrasting below. Stipules wine red, 2 per node, interpetiolar, erect to patent, 12-23 × 3.5-10.5 mm, broadly ovate and slightly falcate, acute, entire or with 1-2 short lateral teeth, slightly veined, sparsely hairy outside with +/- appressed hairs 0.3-1 mm long, glabrous inside. Inflorescences axillary, solitary at each node and borne in the axil of the reduced leaf, densely glomerulate to very shortly cymose, 1.3-1.7 cm long; peduncle very short and usually hidden by the stipules, 0.2-0.5 cm long, with same indumentum as the stems; flowering part 1.2-1.4 × 1.7-2.3 cm; ramifications not or hardly distinct, <0.1 cm. Bracts wine red, numerous, decreasing in size from the base to the apex of the inflorescence, not clearly forming an involucre, entire or shortly dentate, sparsely appressed-hairy outside, glabrous or with very sparse short hairs near the apex inside; lower pair of bracts broadly ovate, shortly connate at base for c. 1 mm and acute at apex, 11-11.5 × 5-7 mm; upper bracts lanceolate, free, acute, 6-11 × 0.5-2.5 mm, resembling the calyx lobes. Flowers (4-)5-merous; pedicels very short, <1 mm long, densely hairy. Calyx wine red, with short tube c. 1 mm; lobes acute, narrowly lanceolate, erect to oblique at anthesis and +/- bending outwards at apex, 5-6 × 0.6-1 mm, sparsely hairy outside with hairs 0.5-1.5 mm long, glabrous inside except short sparse hairs near their apex, alternating with short colleters at their base. Corolla pale buff in bud, pure white at anthesis and later fading to brown; tube narrow and almost cylindrical, 6 × 1.5 mm; lobes triangular, patent, 2 mm long; outside of corolla with short, c. 0.5 mm long stiff hairs on lobes and upper 1/4th of tube, otherwise glabrous; inside of corolla with a dense beard of (0.7-) 1-1.2 mm long moniliform hairs in throat and upper part of tube, and a separate ring of shorter hairs inside the tube just above mid-height. Stamens included, inserted c. 1.5 mm below throat of corolla tube; anthers subsessile, c. 1 × 0.3 mm, shortly apiculate. Ovary c. 2 mm long, densely covered with long appressed stiff hairs, 2-locular in cross-section. Disk shortly cylindrical, c. 0.5 mm, glabrous. Style bifid, included, about equalling the anthers, glabrous, 5.5 mm long including the 1.5 mm long stigmas, these dorsally compressed and rounded at apex. Fruits dark purple outside, with purple flesh, ovoid, with persistent calyx, 12-17 × 8-11 mm in life, villous with patent hairs 1-2 mm long, very shortly pedicellate (pedicel c. 1 mm long). Seeds numerous, dark brown, polygonal, c. 1 × 0.5 mm, the surface with dense parallel striations.

Etymology. – The species is named after Golgotha Hill in the Mabounié region, where it was first discovered, and in the vicinity of which all known subpopulations occur.

Distribution and ecology. – Sabicea golgothae is apparently endemic to the Mabounié region in West-Central Gabon ( Fig. 4 ), where it is known from three very close sites. The new species grows in half-shaded forest edges along tracks, where it locally forms dense populations.

Conservation status. – The EOO of S. golgothae is estimated as 0.608 km ² and the AOO as 12 km ², respectively within the thresholds for “Critically Endangered” and “Endangered” under Criteria B1 and B2. The species is known from three subpopulations (in addition to the two subpopulations from which specimens were taken, a third was observed at 0°46’09”S 10°32’07”E) which represent a single location in the sense of IUCN, and all three occur in the mining concession. One of these subpopulations at least is under immediate threat in the mining project. A decline in the EOO, AOO, extent of habitat and quality, number of subpopulations and number of individuals can therefore be predicted. Sabicea golgothae should thus be assigned a preliminary status of “Critically Endangered” [CR B1ab(i,ii,iii,iv,v)].

Notes. – Sabicea golgothae is very close to S. mabouniensis described below. Both species also resemble S. medusula K. Schum. ex Wernham , S. mildbraedii Wernham , and S. sthenula (N. Hallé) Razafim. et al. All these species have in common a low creeping habit, strong anisophylly (in S. sthenula and some rare variants of S. mildbraedii , the anisophylly is even extreme, with a single leaf per node) and a 2-locular ovary. The major differences between them are summarised in Table 1 .

Sabicea medusula , S. mildbraedii and S. sthenula all differ from S. golgothae in having truly sessile inflorescences, and a green to whitish calyx. In S. golgothae the peduncle, although short, is always present, and the calyx is wine red; the fruits are also conspicuously larger than in the three other species.

From S. mabouniensis , S. golgothae can be distinguished by the acute to obtuse (not cordate) leaf bases, strongly discolorous leaves (with the indumentum completely obscuring the under surface, except on old leaves), more condensed inflorescences with shorter peduncles, the deep wine red colour of its bracts and calyces, and the entirely white corollas with longer hairs in the throat. These differences are slight, but appear to be constant in the subpopulations we have seen. Since the two taxa occur in the same area, only a few kilometers away from each other, and without apparent habitat discontinuity or barriers to dispersal, it seems appropriate to treat them as separate species rather than subspecies. The apparent difference in the internal indumentum of the corolla tube between S. golgothae (two separate rings of hairs) and S. mabouniensis (a single continuous ring) may not be significant, since we have found other Sabicea species (e.g. S. mildbraedii ) to be variable in this respect.

The flowers of S. golgothae , with their anthers and style at same level, appear to be isostylous. This would be exceptional in a genus where distyly is otherwise the rule. However, since only the type collection bears open flowers, more material would be needed to confirm this character.

Paratypus. – GABON. Moyen-Ogooué: Mabounié, Golgotha , 0°45’55’’S 10°32’49’’E, 31.X.2014, Lachenaud, Bidault & Lissambou 2106 ( BR, BRLU, LBV, MO).

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. 2. – Sabicea golgothae O. Lachenaud & Zemagho.A. Habit; B. Node with stipules and reduced leaf; C. Detail of lower leaf surface; D. Inflorescence; E-F. Bracts; G. Flower; H. Longitudinal section of flower; I. Mature fruit; J. Cross-section of fruit. [Lachenaud et al. 2116, BRLU] [Drawing: Antonio Fernandez]

Fig. 3. – Seed of Sabicea golgothae O. Lachenaud & Zemagho, viewed in electron microscopy. A. Entire seed; B. Detail of seed surface. [Photos: Iris van der Beeten]

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