Mezoneuron mindorense Merrill

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

13. Mezoneuron mindorense Merrill

Phillip. J. Sc., Bot. 3: 232. 1908.

Type :— PHILIPPINES, Mindoro, Pinamalayan, Oct. 1906, For. Bur. Merritt 5383 (PNH†)

Neotype (here designated):— PHILIPPINES, Mindoro , Pinamalayan, 20 Oct. 1906, Merritt s.n., For. Bur. no. 479, L (L0651589!)

Synonym. Mezoneuron mindorense Merr. var. inermis Merr. Phillip. J. Sci., Bot. 232. 1908.

Type:— PHILIPPINES: Mindoro, Bulalacao, 8 Sep. 1906, Bermejos 1514. Syntypes BO, GH, K, (K000264160!), PNH, NY (00004517!), US .

Climber, height unknown. Stems with scattered small recurved prickles to 3 mm; glabrous. Stipules linear to oblong, the apex acuminate, or triangular, ca. 1 × 1–2 mm, glabrous. Leaves with (6–) 10–13 pairs pinnae; 8–12 pairs leaflets per pinna; petiole 2.8–5.5 cm; leaf rhachis 11–30 cm, with recurved prickles paired at pinna insertion points, sometimes in threes, and sometimes scattered on the internodes, or leaf unarmed; pinnae 4.5–8 cm; leaf and pinna rhachis both channelled or ridged on the upper side, with sparse whitish to pale orange tomentose hairs, glabrescent, the hairs mostly on the upper (adaxial) side, petiole with sparse whitish tomentose hairs on the upper (adaxial) side. Leaflets opposite or subopposite; terminal leaflets oblong to obovate, base sometimes oblique, apex rounded, obtuse, or retuse, mucronulate, 0.8–2.0 × 0.5–1.0 cm; lateral leaflets oblong, base sometimes oblique, apex rounded, obtuse or retuse, mucronulate, 1.0–2.2 × 0.4–0.9 cm; all leaflets with upper surface glabrous, lower surface glabrous or sometimes with few hairs on petiole and extending on to a small basal area of leaf blade; 2˚ venation anastomosing, 3˚ venation reticulate, veins indistinct above, more clearly visible below. Inflorescence an axillary or terminal panicle; pedicels 9–14 mm, articulated 0–1 mm below hypanthium; all parts (axes, pedicels, calyx) sparsely orange tomentose, hairs short, on pedicels slightly denser around articulation. Bracts persistent, triangular, ca. 1–2 × 1–1.5 mm, glabrous, or tomentose on margins; bracteoles caducous, 3–4 × 0.5–1 mm, lanceolate, tapering to an acute apex, sparsely pubescent on inner surface, glabrous or very sparsely tomentose on outer surface. Flowers with a strongly asymmetric hypanthium, this wider on side of median petal, 1–2 mm × 5–8 mm; lower calyx lobe 6 × 4 mm, other lobes 4–6 × 2–3 mm. Median petal strongly reflexed backwards, 7–8 × 4 mm, blade obovate, 4 × 4 mm, claw oblong, 5 × 3 mm, with hairs along outer edges of claw, otherwise glabrous. Upper lateral petals obovate to suborbicular, ca. 8 × 7 mm, including claw 1 mm long. Lower lateral petals obovate to suborbicular, ca. 8 × 7 mm, including claw 1 mm long. Stamen filaments 12–13 mm long, orange tomentose on the basal ⅓ to ½, or along most of length; anther 1–1.5 mm long. Ovary 3–5 mm long, style ca. 10 mm long, both glabrous, stigma funnel-shaped, ca. 1 mm wide, the rim papillate. Fruit elliptic, base oblique, apex acute, wing usually arising basally ca. 2–10 mm along central vein, the central nerve extending to form a small mucro, 6.4–8 × 2–2.5 cm, wing 5–6 mm wide; fruit surface glabrous; venation reticulate, raised and visible on fruit body, anastomosing and not or slightly visible on the wing; hypanthium semi-persistent. Seeds 1 per fruit; elliptic, positioned centrally, adjacent to wing, visible in outline on fruit exterior when mature, ca. 7 mm diameter.

Distribution:—Endemic to the Philippines. ( Fig. 14).

Habitat and ecology:—Secondary forests, edge of swamps, thickets, at low altitude.

Phenology:—Flowering April–August, fruiting August–September.

Preliminary conservation assessment:—Extent of Occurrence 95,122.598 km 2 = LC; Area of Occupancy 20.000 km 2 = EN.

Category assigned:—Vulnerable (VU). Although the EOO determines this species to be of Least Concern, consideration of other factors suggests that the level of threat may be higher than this. Only a small number (6) of herbarium specimens have been seen by the present author, suggesting that the species is not common, at least in herbaria. Additionally, the most recent of these specimens was collected in 1953. However, it is also noted that the

A TAXONOMIC REVISION OF MEZONEURON

Phytotaxa 274 (1) © 2016 Magnolia Press • 25

species appears to be able to grow in disturbed or secondary vegetation, and is thus able to survive anthropogenic influences to some extent.

Taxonomic notes:— Note from Hattink 1974: “Specimen FB 479 Merritt, 20 Oct. 1906, Pinamalyan, Mindoro, agrees very well with Merrill’s description (e.g. prickles sometimes in threes), while also the locality is the same. It might have exactly resembled the lost type.”