Oncinotis gabonica O. Lachenaud, 2022

Jongkind, Carel C. H. & Lachenaud, Olivier, 2022, Novelties in African Apocynaceae, Candollea 77 (1), pp. 17-51 : 36-39

Oncinotis gabonica O. Lachenaud , sp. nov. ( Fig. 12 ).

Holotypus: GABON. Ogooué-Lolo: Bambidie , c. 30 km E of Lastoursville, 10.VIII.2000, fl., F.J. & B.J.M. Breteler 15574 (2-part specimen: WAG [ WAG.1662404]! + spirit!; iso-: LBV!, MO) .

Oncinotis gabonica O. Lachenaud differs from its congeners by its relatively long corolla tube (4–5 times as long as the calyx) and short lobes (the tube/lobes ratio about 2:1) and its almost glabrous leaves with conspicuous tuft domatia in the main vein axils and dense subparallel tertiary veins. Other species of Oncinotis have the corolla tube 1–3.5 times as long as the calyx, the corolla lobes 0.7–2 times as long as the tube, the leaves either villose below or if glabrous with domatia of the pit type (or absent), and the tertiary leaf veins laxer and usually reticulate.

Lianas woody with slender stem. Branchlets cylindrical, 1 mm thick, with short and moderately dense fulvous indumentum of simple crisped hairs c. 0.3 mm long. Leaves opposite; blade narrowly obovate to narrowly elliptic, 9– 15.5 × 3.6–5.3 cm, acute at base, abruptly acuminate for 0.8– 1.2 cm at apex, thinly papery, glabrous except domatia and very sparse simple hairs on midrib and secondary veins below, drying olive green; midrib impressed on upper side, prominent below; secondary veins 7–11 pairs, strongly curved and forming prominent loops 2– 3 mm from leaf margin; tertiary veins dense, subparallel, prominent and concolorous on lower leaf surface; domatia present as conspicuous tufts of rufous hairs in main vein axils; petiole 0.5– 1 cm long, pubescent on upper side with same indumentum as twigs and bearing a pair of colleters at junction with leaf blade, glabrous on lower side. Inflorescences axillary and paired at nodes, thyrsoid, 1.5–3.4 cm long, with indumentum similar to twigs but denser; peduncle 0.5–1.5 cm long, rachis 0.7–1.2 cm long, main branches 0.2–0.5 cm long; bracts minute, narrowly triangular, 0.5–1.2 × 0.2–0.5 mm, pubescent. Flowers 5-merous; pedicel 1–2 mm long, with short fulvous crisped hairs. Calyces purplish, with 5 imbricate ovate lobes, 1–1.2 × 0.5–0.7 mm, obtuse to subacute at apex, pubescent outside, glabrous inside. Corollas purplish outside and pale brownish-green inside; tube narrowly infundibuliform, 4–5 × 1.8–2 mm, slightly constricted at apex, covered outside (except at very base) with short patent or slightly retrorse hairs, villose inside with slightly retrorse hairs from insertion of stamens to throat; lobes overlapping to right, narrowly elliptic, 2–2.5 × 0.7–1 mm, rounded at apex, pubescent outside like tube on part exposed in bud, glabrous inside; flower bud fusiform, obtuse at apex; throat with 5 erect appendages 0.5–0.8 × 0.2 mm, alternating with lobes. Stamens fully included, inserted c. 1 mm above base of corolla tube, subsessile; anthers 2.3 × 0.4 mm, basally with rounded caudicles, acuminate at apex, glabrous. Pistils included; ovaries ± cylindrical, 0.7 mm long, pubescent at apex, 2-carpellate; disk annular, 0.5 mm high, glabrous; styles included, 1.5 mm long, glabrous, fusiform and inflated in median part, attenuate at apex and shortly bifid for 0.25 mm. Fruits unknown.

Distribution, ecology and phenology. – Only known from the type locality in east-central Gabon ( Fig. 8B ), where it was collected once in secondary lowland evergreen forest. Its area of

O. gabonica O. glabrata O. gracilis O. hirta O. pontyi O. tenuiloba villose, hairs

shortly villose, hairs glabrous to puberulous to Twig indumentum glabrous mostly

pubescent mostly simple puberulous sparsely villose

branched

Leaf texture papery coriaceous papery papery coriaceous papery glabrous glabrous glabrous

glabrous villose below both sides or sparsely

(or veins (or midrib

(except domatia (sometimes also villose, hairs pubescent

Leaf pubescence sometimes sometimes

and veins above), hairs mostly below (and puberulous puberulous

below) mostly simple branched sometimes on below) below)

midrib above)

lax to rather

dense, very lax, lax, reticulate to

Tertiary veins lax, reticulate dense, lax, reticulate

subparallel reticulate subparallel

reticulate conspicuous conspicuous pits, ciliate or hair tufts, often hair tufts, often conspicuous Domatia ciliate pits hair tufts not, or absent obscure obscure ciliate pits (rarely absent)

Sepal length [mm] 1–1.2 1.5–3.6 0.9–2.2 1.2–2.6 0.8–2.1 1.2–3.2 Corolla tube length [mm] 4–5 2.5–4.7 2.5–3.2 2.7–3 2.2–3.8 2.5–3.8

Corolla tube/calyx ratio 4–5 1.1–1.4 1– 3.5 1–1.6 1.6–3.1 1.1–2.4

2.3–5.8 × 2.3–2.8 ×

Corolla lobes [mm] 2–2.5 × 0.7–1 3.2–6.2 × 0.7–1.5 1.7–5.8 × 1–1.7 4.2–7.3 × 0.7 –1.5 0.9–2.5 0.8–1.2

Corolla lobe/tube ratio c. 0.5 1–1.8 1–2

0.7–1.1 0.8–1.7 1.3–1.9

Corolla lobe

c. 2.5 2–2.7 (2.1–)2.6–6.9 1.9–3.1 1.5–4.7 3.5–6.5 length/width ratio

[Breteler et al. 15574] [Drawning:A. Fernandez]

origin is relatively well-explored, and in the absence of further records the species is certainly rare in that area. Flowers have been collected in August, during the main dry season.

Conservation status. – This species is known from a single collection that represents one occurrence and one population. Due to the important forest cover in the area, we consider this occurrence as extant. Based on a 2 × 2 km cell size, its Area of Occupancy [AOO] is estimated as 4 km ², which falls under the threshold for “Critically Endangered” status under Criterion B2. Its Extent of Occurrence (EOO) cannot be calculated. The only known occurrence is located within an active logging concession. It is unclear whether logging itself represents a current threat to the species, since little is known of its ecological requirements, and many liana species (including other Oncinotis ) may benefit from moderate levels of forest disturbance. However, considering the species’ apparently very restricted range, other activities related to the concession (such as the building of roads or other infrastructures) may represent a future threat. Oncinotis gabonica is therefore assessed as “Vulnerable” [VU D2].

Figures

Fig. 12. – Oncinotis gabonica O. Lachenaud. A. Flowering branch; B. Leaf from below showing venation; C. Domatia; D. Young branch; E. Flower; F. Flower (opened) showing pistil and anthers.

Fig. 8. – Distribution maps. A. Landolphia anthonii Jongkind (triangles), L. persooniana O. Lachenaud & Jongkind (circles) and L. verrucosa Jongkind & O. Lachenaud (stars). B. Landolphia glandulosa (Pellegr.) Pichon (stars), L. obovata O. Lachenaud & Jongkind (circles) and Oncinotis gabonica O. Lachenaud (triangle).