Sabicea desseinii 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 : 278-282

Sabicea desseinii Zemagho, O. Lachenaud & Sonké , spec. nova ( Fig. 1A–C , 2 , 3A–B ).

Holotypus: GABON. Ogooué-Ivindo: Peripheric area (NE) of Mwagna National Park , close to Mabekwe camp , 0°35'49"N 13°49'57"E, 506 m, 19.I.2018, fl. & fr., Texier et al. 1895 ( MO!; isotype: BR!, BRLU!, LBV, P, WAG!).

Inflorescentiis capitatis ad nodos defoliatos saepe natis, calyce tubo conspicuo sed lobis longioribus, stipulis reflexis, ramulis foliisque indumento hirsuto Sabicea geophiloide Wernham , S. pilosae Hiern et S. speciosae K. Schum. similis. A S. geophiloide differt calycis tubo intus dense villoso (nec glabro), corollae tubo 22‒27 mm longo (nec 14‒20 mm) et extus longe villoso (nec pilis appressis brevibus munito), ramis foliisque indumento densiore et in sicco rufescente (nec albido). A S. pilosa calycis lobis anguste lanceolatis 0.7‒1.5 mm latis intus villosis et statu fructifero patentibus (nec ovatis, 1.8‒5 mm latis, intus glabris et statu fructifero erectis), a S. speciosa corolla alba (nec rubra), bracteis rubris vel rubrescentibus (nec viridibus), calycis lobis pilis longioribus 1‒2.5 mm (nec 0.5‒ 1 mm) munitis, et ab ambabus inflorescentiis 6‒15-floris (nec 1‒5-floris) bracteis 4 (nec 2) cinctis bracteolisque carentibus distinguitur.

Twining woody liana, up to 3 m tall; young stems cylindrical, 1‒3 mm thick, hirsute, with stiff hairs 1‒3 mm long, often intermixed with much shorter uncinate hairs; older stems 4-sulcate, the bark peeling in strips. Stipules interpetiolar, ovate, 6‒ 20 × 3.5‒8 mm, acute to obtuse at apex, recurved backwards, hirsute outside, glabrous inside except at the base, persistent. Leaves opposite, equal; petiole 0.5‒4 cm long, with same indumentum as the stems; leaf-blade elliptic to obovate, 5‒13.5 × 2.6‒6.2 cm, cuneate to rounded at base, acuminate at apex, papyraceous, green on both sides but markedly paler below, drying olive green to olive brown; both surfaces hirsute, with hairs 0.5‒ 1.2 mm long, denser below; secondary veins 7‒12 pairs, markedly curved and ascending, eucamptodromous; tertiary veins darker and conspicuous below, forming a dense reticulum with areolae c. 1 mm in diameter. Inflorescences usually on old leafless stems, more rarely axillary, solitary, capitate and involucrate, 6–15-flowered; peduncle 0.2–0.5 cm long, hirsute; involucre consisting of two pairs of free bracts, these red to greenish-red, ovate, 6.5‒ 13 × 5‒ 8.5 mm, acute at apex, the inner pair often narrower than the outer, hirsute outside, glabrous inside except at the base, persistent. Flowers 5-merous, sessile, heterostylous. Calyx red to greenish-red; tube 2‒3 × 2‒3 mm at anthesis, accrescent to 5‒7 mm long in the fruiting stage, hirsute to densely appressed-pubescent outside, densely villose with appressed hairs inside; lobes lanceolate, 10 ‒15 × 0.7‒ 1.5 mm, acute at apex, ± erect at anthesis and becoming patent afterwards, hirsute with stiff hairs 1‒2.5 mm long on the margin (and sometimes more sparsely on both surfaces) and shorter appressed to half-erect hairs 0.5‒1 mm long inside (sometimes also outside) and a basal area inside with very dense appressed hairs in continuation of the tube. Corolla white; tube 22‒27 mm long × 1‒1.5 mm wide at base and 2‒3 mm wide at apex, almost cylindrical, villose outside (except at the base) with patent to appressed long silky hairs 1 ‒1.5 mm long often intermixed with shorter crisped hairs, sparsely pubescent inside except at the very base; lobes triangular, 2‒ 3 × 1.2 mm, outside with same indumentum as the tube, inside glabrous. Stamens included for their whole length, inserted around the upper 1/3rd of the corolla tube (long-styled flowers) or included except for the tip, attached a little below throat (short-styled flowers), subsessile; anthers c. 4 × 0.4 mm. Ovary 1.5‒2 mm long, 5-locular, densely villose with stiff appressed to ± patent hairs 1 ‒ 2 mm long. Disk cylindrical, c. 0.3 mm long, glabrous. Style 5-lobed, exserted, c. 29 mm long (long-styled flowers) or included, c. 15 mm long (short-styled flowers), 5-lobed at the apex, the stigmas linear, 5‒ 5.5 mm long, papillose, otherwise glabrous. Fruits bright red, ellipsoid, 11.5‒14 × 8.5‒13 mm when dry, hirsute to appressed-pubescent, crowned with persistent calyx, on pedicels 1‒2.5 mm long. Seeds polygonal, pale brown, 0.5‒0.7 mm long, the surface with close parallel striations.

Etymology. – Named after Dr. Steven Dessein, the Director of the Botanic Garden Meise, in recognition of his active support to the authors.

Distribution, ecology and phenology. – Lower Guinea subcentre of endemism (WHITE, 1979). This species occurs in southern Cameroon, Equatorial Guinea ( Rio Muni) and north-eastern Gabon ( Fig. 4 ); it may be expected in adjacent Republic of Congo. It occurs in secondary rainforest, up to 530 m in altitude, sometimes on seasonally flooded soils, and is locally common in Cameroon (J. & A. Raynal 9859) but apparently rare elsewhere. Flowers have been collected in October, November and January; fruits in January, February and July.

Conservation status. – The extent of occurrence (EOO) of S. desseinii is estimated to be 33,344 km ² (exceeding the limit for “Vulnerable” status under criterion B1) and its area of occupancy (AOO) to be 28 km ² (within the limit for “Endangered” under criterion B2). The species is restricted to Atlantic Central Africa and is known from eight specimens representing seven subpopulations. One of these occurs in a protected area, the Monte Alén National Park in Equatorial Guinea; the other subpopulations are unprotected and exposed to deforestation for agriculture and mining. Even though the species occurs in secondary forest, and thus tolerates a certain degree of habitat degradation, the level of human pressure in its range leads us to anticipate a decline in the extent and quality of habitat, number of locations, number of individuals, and thus EOO and AOO. The seven subpopulations represent seven “locations” (sensu IUCN, 2012) and the species qualifies for “Vulnerable” status [VU B2ab(i,ii,iii,iv,v)] using the IUCN Red List Categories and Criteria ( IUCN, 2012).

Notes. – Sabicea desseinii superficially resembles S. speciosa K. Schum. , but is probably more closely related to S. geophiloides Wernham and/or S. pilosa Hiern. All these species have in common (sub)capitate inflorescences that are often borne on older stems below the leaves, a calyx tube well developed but shorter than the lobes, a relatively long corolla tube, reflexed stipules, and a hirsute indumentum usually covering most of their organs (though some variants of S. pilosa are almost glabrous). The differences between these four species are summarised in Table 1 . Sabicea desseinii also resembles S. gabonica (Hiern) Hepper in its inflorescences and calyces, but the latter species has erect stipules, stems and leaves with appressed pubescence, and inflorescences borne on young leafy stems and usually surrounded by a single pair of bracts, these green in colour.

The only specimen from Gabon was chosen as type since it is the most complete (with both flowers and fruits) and has numerous duplicates. It differs slightly from the rest of the material (from Cameroon and Equatorial Guinea) by the appressed (vs patent) indumentum of the calyx tube, ovaries and fruits, and the slightly shorter indumentum of the stems, but in other characters all collections agree very well and their conspecificity is beyond doubt. The colour of the bracts and calyces may vary from deep red to pale reddish-green in the same population ( Fig. 1A–B ).

Paratypi. – CAMEROON. South: Station du Cacaoyer de N’koemvone , S. of Ebolowa , 14 km on the road to Ambam, on bank of the Seng river , 2°49'N 11°08'E, 16.X.1974, fl., J.J.F.E. de Wilde 7648A ( WAG); près Bidjap , piste pygmée d’Akom II , 75 km W Ambam, 30.XI.1979, fl., Letouzey 15288 ( BR, P, YA); Mékomengona (17 km SW Ambam), au N du village , 20.II.1963, fr., J. & A. Raynal 9859 ( P, YA); 3 Km NE de Bindem, 2º41'27"N 10º47'31"E, 21.VII.2008, fr., Sonké & Simo 5004 ( BR).

EQUATORIAL GUINEA: Inselberg de Bicurga, près du village de Bicurga , 1°35'N 10°28'E, 18.II.2001, fr., Parmentier 1758 ( BRLU); ibid. loco, 24.V.2002, fl., Parmentier & Esono 3159 ( BRLU); Monte Alén, 1°38'N 10°18'E, 10.VIII.2001, fr., Sonké, Esono & Ndong 2498 ( BRLU).

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. 2. – Sabicea desseinii Zemagho, O. Lachenaud & Sonké. A. Leafy stem; B. Inflorescence and portion of old stem; C. Longitudinal section of flower (short-styled); D. Fruit, lateral view (left) and cross-section (right). [A–C: J.J.F.E. de Wilde 7648A, WAG; D–E: Sonké et al. 2498, BRLU] [Drawing: S. Bellanger]

Fig. 3. – Seeds of Sabicea spp. viewed in electron microscopy. A. Sabicea desseinii Zemagho, O. Lachenaud & Sonké: entire seed; B. Sabicea desseinii: detail of seed surface; C. Sabicea jongkindii Zemagho, O. Lachenaud & Sonké: entire seed; D. Sabicea jongkindii: detail of seed surface. [A–B: J. & A. Raynal 9859, P; C–D: Jongkind et al. 12457, BR] [Photos: I. van der Beeten]

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).

Tables

Table 1. – Comparison of morphological characters and distribution between Sabicea desseinii Zemagho, O. Lachenaud & Sonké, S. geophiloides Wernham, S. pilosa Hiern and S. speciosa K. Schum. Characters diagnostic for one species are in bold.

	S. desseinii	S. geophiloides	S. pilosa	S. speciosa
Indumentum of stems & leaves	+/– dense, rufescent when dry	sparse, whitish	dense to sparse, whitish	+/– dense, rufescent when dry
Inflorescences	aerial	usually near the ground	usually near the ground	aerial
Number of flowers per inflorescence	6–15	5–7	(1–)3–5 (but inflorescences often fasciculate)	3–5
Number of involucral bracts	2 pairs	2 pairs	1 pair	1 pair
Bracteoles	absent	absent	1 pair/flower	1 pair/flower
Bract colour	red/greenish red	?	red	green
Bract size [mm]	6–13 × 5–8.5	10–17 × 8–14	6–15 × 3–9	5–8 × 3–5
Calyx tube (inside)	villose	glabrous	villose	villose
Calyx lobes (indumentum) [mm]	long stiff hairs (1–2.5) at least on the margin + shorter hairs at least inside	long stiff hairs (1–1.5) outside, sometimes also inside	stiff hairs (0.5–1.5) outside, inside glabrous	short stiff hairs (0.5–1) on both sides
Calyx lobes (size) [mm]	10–15 × 0.7–1.5 10–15 times longer than wide	5.5–13 × 1–3 4–6 times longer than wide	6–18 × 1.8–5 1.8–4.5 times longer than wide	6–20 × 0.5–1.5 8–20 times longer than wide
Corolla	white	white	white	red
Corolla tube length [mm]	22–27	14–20	18–27	20–26
Corolla indumentum (outside)	long-villose	shortly appressed-pubescent	variable	long-villose
Calyx lobes on fruit	patent	patent	erect	patent
Distribution	Cameroon, Equatorial Guinea, Gabon	Ivory Coast to Cameroon	Cameroon, Equatorial Guinea, Gabon	Nigeria to D. R. Congo