Mendoncia rabiensis Breteler & Wieringa, 2018

Breteler, F. J. & Wieringa, J. J., 2018, A synopsis of Mendoncia (Acanthaceae) in continental Africa including the description of two new species from western Central Africa and a new subspecies from West Africa, Blumea 63 (2), pp. 109-119 : 116-118

8. Mendoncia rabiensis Breteler & Wieringa , sp. nov. — Fig. 4 ; Map 8

By its small leaves resembling Mendoncia gilgiana Benoist subsp. gilgiana , differing by its single-flowered inflorescences and by its indumentum of hispid hairs mixed with some stellate/branched hairs. — Type: Schoenmaker 177 (holo WAG 2 sheets WAG0088063 & WAG0088064 ), Gabon, Ogooué-Maritime, Rabi-Kounga , c. S1°45' E9°57', 22 Nov. 1991 .

Liana. Branchlets hispid mixed with some smaller, stellate and/ or branched hairs, glabrescent and corky ribbed lengthwise when older. Leaves opposite: petiole semi-terete, grooved above, 6–12 mm long, hairy like branchlet; lamina ovate-elliptic, (4–)6–10 by (2–) 3–4 cm rounded at base, acutely 0.5–1.5 cm acuminate at apex, sparsely pubescent both sides on midrib and the 3–4 pairs of main lateral nerves, the latter distinct beneath, glabrescent. Flowers axillary, solitary. Pedicel (in fruit) 20–25 mm long, hairy like branchlet. Bracteoles (in fruit) ovate-elliptic, c. 25 by 15 mm, palmately 4–5 nerved, strigose hispidulous mixed with stellate and/or branched hairs outside, glabrous inside. Calyx in fruit c. 2 mm long, glabrous. Corolla and stamens unknown. Fruit ovoid, 17 by 11 mm, glabrous.

Habitat & Distribution — Tropical rain forest in West Gabon. Altitude 0–100 m.

Additional specimen studied. GABON, Ogooué-Maritime, McPherson 15543

(K), Rabi-Kounga, c. S1°45' E9°57', 22 Nov. 1991.

Conservation status — Mendoncia rabiensis is only known from a single population with probably only a single individual sampled (see notes), in an area that is currently not formally protected. There is some logging in the area, but when Shell will abandon their oil exploitation (as is expected in the short term), and with the construction of a new road from Port-Gentil to the South, the area will be under more severe pressure by wood extraction and settlers. Therefore, the species is assessed as Critically Endangered (CR; 2a, b(ii,iii,v)).

Notes — McPherson 15543 ( K) resembles the holotype in all aspects. It has been collected on the same day, at the same locality, and with the same field notes: ‘liana, bracts and fruits pale green’. We consider it likely the material is derived from the same plant .

Magnaghi & Daniel (2017) saw McPherson 15543 in K bearing already a new annotation label of M. rabiensis by the first author and discuss why they think it fits M. combretoides . It indeed shares with that species relatively small leaves and branched trichomes, however, M. combretoides does not have simple fairly long hispid hairs as are found in M. rabiensis , and it usually has several flowers per axil where M. rabiensis has only one. According to Magnaghi & Daniel (2017) M. combretoides may have small simple appressed hairs as well, but we could not find these.Also, the difference in geography (Upper Guinea vs Gabon) should not easily be put aside.

Figures

Map 8 Distribution of Mendoncia rabiensis Breteler & Wieringa.

Fig. 4 Mendoncia rabiensis Breteler & Wieringa. a. Habit, leafy shoot; b. leaf, under side; c. detail of leaf lower surface; d: detail leaf lower surface at midrib with indumentum; e. leaf pair with young fruit; f. young fruit, one bracteole removed; g. detail of indumentum on bracteole (all: J. Schoenmaker 177, WAG). — Drawing by Hans de Vries.