Mezoneuron hymenocarpum Wight & Arnott ex Prain

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

11. Mezoneuron hymenocarpum Wight & Arnott ex Prain

J. As. Soc. Beng. ii, 66: 233. 1897 (description)

Type :— MYANMAR, Taong Doung, Wallich 5832. Holotype K (K000264174!); isotype BM (BM000958801!)

M. hymenocarpum Wallich ex Wight & Arn. nom. nud. in Wight, R.A. & Arnott, G.A. Prodromus Florae Peninsulae Indiae Orientalis : 283. 1834.

Based on Caesalpinia hymenocarpa Wallich cat. n. 5832 (nomen) 1832.

Synonym. Caesalpinia hymenocarpa (Wight & Arn. ex Prain) Hattink. Reinwardtia 9 (1): 35. 1974.

Synonym. Mezoneuron laoticum Gagnepin. Not. Syst. 2: 208. 1911.

Lectotype:— LAOS, Me Kong , Steung Streng (=Stung Treng), 1866–68, Thorel s.n., P (P 02142674!), Hattink 1974.

Woody climber or scandent shrub to 30 m in length. Stems with scattered recurved prickles, older stems with spine-tipped corky tubercles; glabrous to sparsely whitish tomentose. Stipules persistent, oblong to ellipsoid, sometimes with acuminate apex, 1–2 × 1–5 mm, subglabrous. Leaves with 6–9 (–12) pairs pinnae; (4–) 6–9 (–11) pairs leaflets per pinna; petiole 2.4–9 cm; leaf rhachis (12–) 15.5–30 (–33) cm, with recurved prickles paired at pinnae insertion points and sometimes scattered on the internodes; pinnae opposite or subopposite, 4–10 (–12.5) cm, pinna rhachis sometimes with recurved prickles paired at leaflet insertion points and a sometimes scattered on the internodes, with terminal prickle 1–3 mm; leaf rhachis, petiole, and pinna rhachis sparsely to moderately whitish or pale orange tomentose. Leaflets opposite to subopposite, terminal leaflets obovate or elliptic, base oblique, apex rounded to retuse, 1–3.8 × 0.5–2.2 cm; lateral leaflets oblong to elliptic to slightly obovate, sometimes oblique, especially at base, apex rounded to retuse, 1.0–3.3 (–4.0) × 0.6–2.0 cm; all leaflets with upper surface glabrous or with sparse, semi-appressed, or tomentose, whitish hairs, on base of lamina and midrib, or on entire surface, lower surface usually with sparse, semi-appressed, or tomentose, whitish hairs, these sometimes only on basal midrib, occasionally glabrous. Inflorescence a panicle or raceme, axillary, supra-axillary, or terminal, to 60 cm; sometimes with few recurved prickles on basal parts of axes; axes and pedicels sparsely to densely white or golden to pale orange tomentose; pedicels 6–28 mm, articulated 2–3 mm below the hypanthium, indumentum denser at articulation. Bracts sometimes present, caducous, triangular, ca. 1 × 1 mm, subglabrous to sparsely tomentose; bracteoles caducous, elliptic-lanceolate, tapering to an acute apex, narrowing at base, 1–5 × 1–2 mm, moderately to densely golden or orange tomentose on both surfaces. Flowers with an asymmetric hypanthium 2–4 × 6–12 mm, sparsely to moderately golden tomentose; lower lobe highly cucullate, 9–15 × 4–6 mm, other lobes 4–7 × 3–6 mm; outer surface of lobes moderately to densely golden to orange tomentose, inner surface of lower lobe moderately to densely tomentose, inner surface of other lobes glabrous or with few hairs, sometimes denser at margins. Median petal coriaceous, the blade broadly elliptic to oblong, and distinct narrow claw, strongly reflexed backwards, with transverse flap of tissue between claw and blade, this bilobed or dentate; blade 4–5 × 4–14 mm long, claw [3–] 4–5 mm × 1.5–2 mm, the whole 7–10 mm long; few hairs along margins of claw, and along margin of the flap of tissue. Upper lateral petals orbicular to obovate, 7–15 × 6–13 mm, including claw 1–2 mm; glabrous apart from few hairs on inner surface of claw. Lower lateral petals orbicular to obovate, 7–15 × 9–13 mm, including claw 1–2 mm long; glabrous apart from few hairs on inner surface of claw. Stamen filaments [7–] 9–18 mm long, vexillary stamen shorter than the others, glabrous or nearly so, other 9 stamens moderately to densely orange villous on the basal ½ on inner surface; anthers ca. 3 mm long. Ovary ca. 5–8 mm long, style ca. 7–14 mm long, both glabrous, stigma broadly funnel-shaped, ca. 1 mm wide, the rim papillate. Fruit oblong-elliptic, base cuneate, sometimes oblique, apex acute, sometimes oblique, (5.5–) 6.5–17 × 1.9–4.6, wing 4–16 mm wide; fruit surface glabrous; venation reticulate, raised and visible on the fruit body, anastomosing and slightly visible on the wing; hypanthium semi-persistent. Seeds 2–6 per fruit, elliptic to orbicular, often clearly visible in outline when mature as concave or convex shape in the fruit, adjacent to and perpendicular to the wing, pale brown.

Distribution:— India, Sri Lanka, Myanmar, Thailand, Vietnam; Malesia: Java, Lesser Sunda Islands, Philippines; Australia. ( Fig. 12 ).

Habitat and ecology:—Deciduous forest, evergreen forest, primary or secondary; open disturbed thicket, roadside; granite, sandstone, shale or limestone bedrock. Elevation to 850m. Occurs in regions that experience a dry season.

22 • Phytotaxa 274 (1) © 2016 Magnolia Press

CLARK

Phenology:— India, Sri Lanka: flowering September–November, fruiting December. Myanmar: flowering August, fruiting October. Thailand, Laos, Vietnam: flowering July–January, fruiting August–May. Malesia: flowering April, fruiting May–November. Australia: flowering time unknown, fruiting April–August.

Preliminary conservation assessment:—Extent of Occurrence 10,239,581.796 km 2 = LC;

Area of Occupancy 220.000 km 2 = EN.

Category assigned:—Least Concern (LC).

Figures

FIGURE 12. Distribution of M. hymenocarpum in South East Asia.