Derris laotica Gagnep.

         Lianas, 6–10 m high. Twigs 3–4 mm diam., striate, lenticellate, glabrous.. Stipules ovate-triangular, 1.3–1.5 by 0.9–1.3 mm, outside glabrous to thinly sericeous, especially at the base, margin ciliate, inside glabrous. Leaves usually trifoliate, petiole 1.5–5 cm long, striate, glabrous or with few hairs; rachis 0.6–1.3 cm long, striate, glabrous or with few hairs; pulvinus 2–5 mm long, glabrous to thinly hirsute, especially at the base. Stipellae absent or rarely present, acicular, 0.5–1 by 0.2 mm, glabrous. Leaflets subcoriaceous; terminal one elliptic to obovate, 5.5–6 by 2–3.5 cm, length/width ratio 1.7–2.7, base rounded to subcordate (cuneate in former var. virens), apex slightly acuminate, acumen 2–5 mm long, rounded, upper surface glabrous, lower surface glabrous or with widely scattered appressed hairs, midrib flat to slightly raised in a furrow above, nerves slightly raised above, 6–8 per side, 3–6.5 mm apart, not reaching the margin but curving towards the apex, anastomosing near the margin, venation reticulate; lateral leaflets mostly like terminal one, (narrowly) elliptic to ovate, 3.3–7.5 by 0.9–3.2 cm, length/width ratio 2.3–3.6; pulvinus 1–2 mm long, glabrous. Inflorescences axillary pseudoraceme/pseudopanicle, rarely terminal, 6.5–20 cm long; peduncle 0–1 cm long, thinly strigose; lateral branches up to 18.5 cm long. Bracts subtending brachyblasts narrowly elliptic to ovate, 0.7–1 by 0.3–0.4 mm, outside glabrous, margin ciliate to fimbriate, inside glabrous except for some hairs at the base; bracts subtending flowers ovate to triangular, 0.6–0.7 by 0.4–0.5 mm, outside glabrous, margin ciliate to fimbriate, inside sericeous. Brachyblasts slender, cylindrical, 5–10 mm long, with 2 (–3) flowers at the apex. Pedicels 3–5 mm long, glabrous or thinly sericeous. Bracteoles at the upper part of the pedicels, (narrowly) ovate, 0.5–0.6 by 0.2–0.4 mm, outside glabrous or thinly sericeous, margin ciliate to fimbriate, inside glabrous or thinly sericeous. Calyx cupshaped, 2.5–2.7 mm high, outside glabrous, margin ciliate, inside sericeous at apex, tube 2–2.2 mm high; upper lip indistinct or sometimes with 2 shallow notches; lateral lobes triangular, ca. 0.5 by 1.9–2.1 mm; lower lobe triangular, 0.5–0.7 by 1–1.5 mm. Corolla pink. Standard: claw 2.5–2.8 mm long; blade broadly ovate to orbicular, 8–8.5 by 7–7.8 mm, apex emarginate, basal callosities indistinct or absent (in var. virens), both sides glabrous. Wings: claw 2.8–3 mm long; blade elliptic, 6.5–7 by 1.8–2 mm, apex rounded, upper auricle 0.5–0.6 mm long, both sides glabrous, lower auricle indistinct, lateral pocket indistinct or absent. Keel petals: claw 2.9–3 mm long; blade boat-shaped, 7–9 by 3.5–3.7 mm, apex rounded, both sides glabrous, upper auricle ca. 0.5 mm long, sometimes indistinct, lateral pocket 1.8–3 mm long. Stamens monadelphous, with basal fenestrae, 11–13 mm long, free part 2.5–4.5 mm long, glabrous or with some hairs at apex; anthers 0.5–0.6 by 0.3–0.4 mm, glabrous. Disc annular or indistinct, 0.5–1 mm high, glabrous. Ovary 5.8–7 mm long, outside sericeous, inside glabrous; stipe up to 0.5 mm long, sometimes indistinct; ovules 4 or 5; style 6–8 mm long, sericeous at lower part. Pods and seeds unknown.