Mezoneuron ouenensis (Guillaumin) R. Clark

Clark, Ruth P., 2016, A Taxonomic Revision of Mezoneuron (Leguminosae: Caesalpinioideae: Caesalpinieae), Phytotaxa 274 (1), pp. 448-450 : 448-450

20. Mezoneuron ouenensis (Guillaumin) R. Clark in Clark, R. & Gagnon, E. Phytotaxa 207(1): 68–92. 2015.

Holotype:— NEW CALEDONIA: 27 ‘7bre’ 1868, Balansa, B. 312 (fl.) P (P00379653!).

Basionym. Caesalpinia ouenensis Guillaumin , Bulletin de la Société Botanique de France 83: 308–309. 1936.

Shrub, 1– 2 m. Stems without recurved prickles, glabrous. Stipules unknown. Leaves bipinnate, unarmed; pinnae 2–3 opposite pairs, paripinnate; leaflets opposite, 1–2 pairs per pinna; petioles 2.5–3.5 cm; rhachis 6.5–7.5 cm; pinnae 1.5–3.8 cm; leaf rhachis, petiole and pinna rhachis glabrous. Leaflets orbicular to obovate, base oblique, apex rounded; 3.3–5 × 2.7–4 cm; 2˚ veins anastomosing, visible on both surfaces. Inflorescence an axillary raceme, ca. 7 cm long, all parts glabrous. Pedicels 8–10 mm, not articulated. Bract at base of pedicel 2–3 mm long, lanceolate. Hypanthium ca. 3 mm deep, glabrous, lower calyx lobe ca. 9 × 3 mm, other lobes ca. 6–7 × 3 mm, glabrous. Median petal size unknown, lateral petals ca. 11–13 mm long. Stamen filaments ca. 12–15 mm long, glabrous; anthers c. 1 mm long; ovary not seen. Fruit unknown.

Distribution:—Endemic to New Caledonia. Known only from the type specimen, collected on Ile Ouen (South Province). ( Fig. 23).

Habitat and ecology:—Single known specimen found on the edge of a stream. Vegetation not stated on specimen label, inferred to be maquis on ultramaphic substrate, as this is the only native vegetation type on Ile Ouen.

Phenology:—Unknown.

Preliminary conservation assessment:—Known only from a single locality, so no AOO or EOO values can be generated.

36 • Phytotaxa 274 (1) © 2016 Magnolia Press

CLARK

Category assigned:— Critically Endangered CR B1ab(iii)+2ab(iii) ( PE). Mezoneuron ouenensis is known from a single herbarium specimen on the Ile Ouen (ultramafic substrate) collected in 1868. Ile Ouen, the type locality, is a small island (c. 8.7 × 7.2 km), which has been subject to anthropogenic disturbance (mining activities & bush fires etc.) that may have destroyed the population from which the type specimen was derived. It is therefore assigned a status of Critically Endangered ( CR) with criteria B1ab(iii)+2ab(iii)) with the tag Possibly Extinct with a continuing decline of the habitat quality. It is recommended to implement prospection of the island in order to confirm its probable extinction or implement urgent conservation actions if it was relocated. (RLA Flore NC 2016)