THAI FOREST BULLETIN (BOTANY) 36
Steud,: Van Thuan, Fl. Camb. Laos Vietnam 17: 36. 1979.— M. nigricans sensu auctt. var. hainanensis (Hayata) Wilmot-Dear, Kew Bull. 39: 43. 1984.— M. nigricans sensu auctt., var. hongkongensis Wilmot-Dear, Kew Bull. 39: 45. 1984. Type: China, Hong Kong [New Territories, Lau 3234 (holotype K!; isotype HK!)].—M. interrupta sensu Averyanov in Averyanov et al., Contrib. Viet. Isl. Fl. Veg.:58. 1988; non Gagnep.
Vegetatively very similar to M. stenoplax but more variable; stems and leaves glabrous or sparsely adpressed-hairy. Leaves with terminal leaflet very variable in size, 4.5– 12 by 2.5–5.5 cm, elliptic or elliptic-obovate, lateral veins (3–)5(–7) pairs; stipels 1–2 mm long. Inflorescences 4–40 cm long, unbranched, ultimate branchlets spaced through most of length but absent from basal part, knob-like; bracts often present in flowerless part of axis, broadly ovate, long-acuminate, 20–30 by 10–16 mm, upper bracts of different form, broadly elliptic or obovate with rounded and often hooded apex, 10–20 by 8–18 mm; bracteoles narrowly obovate or ± linear to narrowly elliptic, 9–13 by 2–4 mm; pedicels 0.8– 1.3 cm, these and main axis with dense adpressed, fine, pale pubescence. Calyx with hairs like the axis and abundant red bristles, tube broadly cup-shaped, 0.6–1 by 1–1.3 cm, lobes long, narrow, acuminate, lowest 8–10 mm, laterals 5–6 mm long, all 2–3 mm wide. Corolla purple (rarely white), standard 2.7–3.2 cm, wing (4.2–) 5–5.5 by (8–)12–15 mm, tapering to acute apex, keel ± equalling wing. Fruit leathery, varying widely in shape from broadly asymmetrically oblong with very convex upper margin, straight lower margin and only 2 seeds to linear-oblong but strongly indented between 3–4 seeds, 7–17 by 3–5 cm, length/ width ratio 2–4:1, markedly laterally flattened, to ca 1 mm thick; surface with abundant irritant red bristles but otherwise glabrescent and rather shiny, lamellae 8–12(–14), very oblique, simple, parallel, thin-textured, not interrupted nor running into wings, uniformly 4– 5 mm high; marginal wings uniformly 8–14 mm wide. Seeds black, 1.7–2(–2.5) & 1.5(–2) cm, strongly laterally flattened; hilum black.
Thailand.— NORTHERN: Chiang Mai [Pooma 289 (BKF)], Tak [Maxwell 94–904 (GH, L)]; SOUTHWESTERN: Prachuap Khiri Khan [Middleton et al. 1255 [white-flowered form] (GH); ibid, HuaiYang, Put 3198 (K., L.)]; SOUTHEASTERN: Chanthaburi [van Beusekom et al. 2058 [form with white keel petals] (C, P)]; PENINSULAR: Surat Thani [Ko Samui, Put 1280 (K. L)].
Distribution.— Vietnam (mainly eastern part), China (Hong Kong, Hainan). Ecology.— Forests, thickets, rocky areas, hedges; low altitude.
Notes.— Only six collections of M. hainanensis have been seen from Thailand (all cited above) and the wide scattering of these few records suggests that it may be overlooked and under-collected. It is easily distinguished in fruit from other lamellate-fruited taxa by its combination of simple lamellae (not bifurcated) and of ± uniform height, running parallel obliquely across the pod face, and a wide and even marginal pod wing. Vegetatively it is ± indistinguishable from M. stenoplax, and two species with bifurcated lamellae, M. interrrupta and M. revoluta. Its flowers are often larger than in M. stenoplax and M. revoluta. M. stenoplax also differs through its lengthened (not knob-like) ultimate inflorescence branchlets, M. revoluta in its often small flowers and in pedicels and axis with minute spreading pubescence, M. interrrupta in its calyx lobes broad-acute with lateral lobes almost equalling lowest and always white flowers (only one collection of M. hainanensis seen with cream rather than purple flowers). The other subspecies, M. hainanensis subsp.