Four new species of Sabicea (Rubiaceae) from tropical Africa, with additional notes on the genus
Zemagho, Lise
Lachenaud, Olivier
Sonké, Bonaventure
Candollea
2018
2018-11-23
73
2
277
293
8Y97Z
Zemagho, O. Lachenaud & Sonke
Zemagho, O. Lachenaud & Sonke
2018
[113,645,1644,1668]
Magnoliopsida
Rubiaceae
Sabicea
Plantae
Gentianales
5
282
Tracheophyta
species
ezangae
sp. nov.
Holotypus: GABON. Moyen-Ogooué: Concession Maurel & Prom, près du Lac Ezanga, 1°05'41"S 10°15'25"E 22.XI.2013, fl., Lachenaudet 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 mtall; young stems cylindrical, 1‒2 mmthick, with a mixed indumentum of soft patent hairs 1.5‒2.5 mmlong and much shorter crispate hairs; older stems with scaling bark. Stipulesinterpetiolar, ovate, 5.5‒10 × 3.5‒6.5 mm, acute at apex, recurved, villose outside, glabrous inside except at the base, persistent. Leavesopposite and equal; petiole 0.4‒2 cmlong, 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 mmlong, intermixed with shorter uncinate hairs; lower surface with mixed indumentum of rather sparse short woolly hairs, and long soft hairs 1.5‒ 2 mmlong (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. Inflorescencesaxillary, solitary, capitate and involucrate, 4 ‒ 5-flowered; peduncle 0.7 ‒6.2 cmlong, 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 mmlong and short crisped hairs, inside sparsely hirsute in the upper half; bracteoles absent. Flowers(4‒)5-merous, sessile. Calyxpale pinkish; tube very short, c. 0.5 mmlong, 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. Corollawhite; tube 16‒18 mmlong × c. 1 mmwide at base and c. 3 mmat 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 mmlong in the throat; lobes triangular, 1.5‒2 × 1.5‒2 mm, reflexed, outside densely silky-pubescent, inside minutely papillose. Stamenshalf-exserted, inserted just under the apex of the corolla tube, subsessile; anthers white, c. 2 × 0.5 mm. Ovaryc. 1.5 mmlong, 5-locular, densely villose with stiff hairs c. 1.5 mmlong. Diskcylindrical, c. 0.7 mmlong, glabrous. Style5-lobed, included, c. 14 mmlong including the c. 2.5 mmlong linear stigmas, the latter papillose, otherwise glabrous. Fruitsand seedsunknown.
Etymology. – Named after Lake Ezanga, in the vicinity of which the species was found.
Distribution, ecology and phenology. – Lower Guineasubcentre of endemism (WHITE, 1979). Only known from the typelocality in west-central Gabon( Fig. 4), near Lake Ezanga (about 50 kmsouth-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 min altitude. The species has never been recollected, although special attention was given to Sabiceaspp.during recent botanical inventories in Gabon. Sabicea ezangaeis flowering in November.
Conservation status. – Sabicea ezangaeis 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 km², 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 Sabiceaspeciesare generally easy to cultivate, an ex situconservation program for S. ezangaemay be recommended.
Notes. – Sabicea ezangaeresembles both S. schaeferiWernhamand S. calycinaBenth.; 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. ezangaeand S. schaeferiare 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. ezangaehave not been collected, and those of S. schaeferiare known in the very young stage only. There is also some resemblance between S. ezangaeand S. gracilisWernham, but the latter has a much shorter corolla tube (c. 8 mmlong 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 Cameroonand Equatorial Guinea( Rio Muni). It is not known whether this species is heterostylous; only short-styled flowers are known so far.
3470697325
2013-11-22
BR
Lachenaud
Gabon
-1.0947223
Concession Maurel & Prom
21
10.256945
5
282
BR0000024387149
1
Moyen-Ogooue
holotype
3470697324
BRLU, LBV, MO, P, WAG
5
282
1
isotype