Mezoneuron ouenensis (Guillaumin) R. Clark, 2015

Clark, Ruth P. & Gagnon, Edeline, 2015, A revision of Mezoneuron (Leguminosae: Caesalpinioideae) in New Caledonia, with perspectives on vegetation, geology, and conservation, Phytotaxa 207 (1), pp. 68-92 : 79-80

Mezoneuron ouenensis (Guillaumin) R. Clark comb. nov.

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

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

Shrub, 1– 2 m. Stems without recurved prickles, glabrous. Stipules unknown. Leaves bipinnate, unarmed, all parts glabrous; 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. Leaflets orbicular to obovate, base oblique, apex rounded; 3.3–5 × 2.7–4 cm; secondary veins anastomosing, visible on both surfaces. Inflorescence an axillary raceme, c. 7 cm long, all parts glabrous. Pedicels 8–10 mm, not articulated. Bract at base of pedicel 2–3 mm long, lanceolate. Hypanthium c. 3mm deep, glabrous, lower calyx lobe c. 9 × 3 mm, other lobes c. 6–7 × 3 mm, glabrous. Median petal size unknown, lateral petals c. 11–13 mm long. Stamens 10, c. 12–15 mm long, glabrous; ovary not seen. Fruit unknown. ( Figure 2 )

Distribution:— Endemic to New Caledonia. Known only from the type specimen, collected on Ile Ouen (South Province). ( Figure 7 )

Habitat and Ecology:— 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:—

Category assigned:— Critically Endangered

Rationale:— M. ouenensis is determined here as Critically Endangered, as it is known only from a single specimen, collected in 1868. Ile Ouen, the type locality, is a small island (c. 8.7 × 7.2 km), which is inhabited and has been subject to anthropogenic disturbance that may have destroyed the population from which the type specimen was derived. There are very few herbarium collections from this island, particularly from recent years. This could indicate either that there is little of interest to collect on the island, which could be a result of destruction of the vegetation, or simply that the island is seldom visited by collectors. A survey of the island is required to verify this assessment.

Figures

FIGURE 2. Illustration of M. montrouzieri, with leaf detail of all species. (a) M. montrouzieri habit, leaf and inflorescence, with detail showing idioblasts on leaf undersurface; flower, side view; flower opened out; petals, inner surface (median, 2 upper laterals, 2 lower laterals); ovary and style; fruit with detail of hairs—drawn from Clark, R.P. 160; (a)(i) M. montrouzieri glabrous ovary; (a)(ii) leaf pinna—drawn from Clark, R.P. 150 (specimen formerly identified as M. deverdiana); (b) pinna of M. baudouinii—drawn from Clark, R.P. 141; (c), (c)(i) pinnae of M. schlechteri (showing variation)–drawn from Clark, R.P., 132, 134; (d) pinna of M. rubiginosum—drawn from McPherson, G. 2089; (e) pinna of M. ouenensis—drawn from Balansa, B. 312. Illustration by Margaret Tebbs.

FIGURE 7. Distribution of M. ouenensis