Mezoneuron rubiginosum (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 : 80-82

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

Basionym. Caesalpinia rubiginosa Guillaumin , Bulletin de la Société Botanique de France 83: 309–310. 1936.

Lectotype (here designated):— NEW CALEDONIA: Boghen, Cribs 982, P (P02969638!); isolectotype: P (P02969637!)

Remaining syntypes:— NEW CALEDONIA: Mount Boakim, Lecard s.n., P (P02969633!, P02969644!)

Liana to 5m. Stems apparently unarmed; sparsely to moderately whitish to ferruginous tomentose. Stipules semi-caducous, triangular, 1–1.5 × 0.5 mm, sparsely tomentose. Leaves bipinnate, rhachis unarmed or with recurved prickles in pairs at pinna insertion points, and sometimes scattered on the internodes, sparsely to densely whitish or ferruginous tomentose; pinnae 4–6 opposite pairs, paripinnate; leaflets opposite, 2–5 pairs per pinna; petiole 4.3–14 cm; rhachis 14.5–25.5 cm; pinnae 4.8–10 cm. Leaflets elliptic to obovate, oblique at base, obtuse to slightly emarginate at apex; terminal leaflets 3.2–5.1 × 2–3.3 cm; median laterals 2.8–5.1 × 1.8–3 cm; secondary veins reticulate, anastomosing, clearly visible on both surfaces; glabrous above, or with few whitish to ferruginous hairs on lower midvein, below glabrous or glabrate, with sparse hairs on petiole and midvein, or sparsely appressed hairy, denser on midvein. Inflorescence an axillary, supra-axillary, or terminal, raceme or few to many-branched panicle, congested, the flowers spaced c. 2–3 mm apart, 12–18.5 cm long, sparsely to densely ferruginous tomentose on peduncle and pedicels. Pedicels 2–3 mm, not articulated. Bracts sometimes singly at base of racemes, triangular, c. 1 × 0.5 mm, moderately to densely tomentose; bracteoles at base of pedicels, 3 × 0.5–1 mm, linear, inrolled, moderately to densely ferruginous tomentose. Hypanthium c. 2 mm deep, sparsely to moderately ferruginous tomentose; lower calyx lobe c. 5 × 2 mm, sparsely ferruginous tomentose, other lobes c. 4 × 2 mm, glabrous or with very few hairs, slightly ciliate on the margins. Median petal 6 × 2.5–3 mm, with a patch or band of ferruginous hairs on inner surface of claw, outer surface glabrous; upper lateral petals 6–7 × 2.5 mm, lower laterals 6–7 × 2.5 mm; all laterals with blade glabrous, claw very sparsely ferruginous tomentose on inner surface or both surfaces very sparsely puberulous. Stamens 10, filaments 6–8 mm, ferruginous tomentose on lower ⅓. Ovary 3–4 mm, densely ferruginous tomentose, style 4–10 mm, moderately ferruginous pubescent along most or all of its length; stigma funnel-shaped, the rim fimbriate. Fruit unknown. ( Figure 2 )

Distribution:— Endemic to New Caledonia. Lifou (Îles Loyauté); Grand Terre, North and South Province, Western side. ( Figure 8 )

Habitat and Ecology:— Wet forest (Appendix 2), on non-ultramaphic soil (collections McPherson 2089, Daniker 2390, Hartley 14975). The species may also occur in sclerophyllous forest, according to the localities of some specimens collected in areas that appear to have been formerly vegetated with sclerophyllous forest ( Jaffré et al. 1998). Due to the imprecise nature of the locality information available, however, it is not possible to confidently establish the vegetation type from which some of the specimens were collected (McKee 26003, Cribs 982, Gervais s.n.). Elevation 100– 800 m.

Phenology:— Flowering October to November, fruiting time unknown.

Preliminary Conservation Assessment:— Extent of Occurrence 16,020.691 km 2 = VU, Area of Occupancy 16.00 km 2 = EN

Category assigned:— Critically Endangered

Rationale:— M. rubiginosum occurs in wet forest on non-ultramaphic soil. It may also occur in sclerophyllous forest, but this cannot be determined with certainty on the basis of the data available.

The specimens available at the time of study were collected between 1886 and 1972 (and date unknown). There has been an ongoing decline in the area of cover of both wet and sclerophyllous forest between the early records, and the present day, and at some of the collection localities the forest appears to have been replaced by savannas and secondary thicket. The assessment generated for this species by GeoCAT based on AOO is EN (Endangered), and based on EOO alone the rating is VU. However, the EOO measurement is somewhat biased by the single specimen collected from the Îles Loyauté, without which it would be EN. On further analysis, taking into account the age of the known specimens, and the depleted forest cover in some of the specimen localities, it appears highly probable that the total number of individuals still in existence is lower than inferred from the AOO and EOO, and that some of the populations have been negatively impacted, or destroyed. On this basis, we conclude that this species is in danger of extinction, and may be appropriately assigned the category CR (Critically Endangered).

Nomenclatural Notes:— The lectotype was selected for being the syntype that most closely corresponds to the species description.

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 8. Distribution of M. rubiginosum