Derris tonkinensis Gagnep.

         Lianas, basal diameter 2–4 cm. Bark thin, smooth, light brown-gray, lenticellate. Stipules triangular, ca. 1.5 x 1–1.5 mm, outside slightly hairy, glabrescent, inside glabrous. Leaves with 5–7 leaflets. Petiole 1.8–4 cm long, grooved above, glabrous, rachis 1.7–4 cm long, pulvinus 2–4.5 mm long. Stipellae absent. Leaflets: subcoriaceous; terminal one elliptic to obovate, 4.5–8.5 x 1.7–3.5 cm, length/width ratio 2.5–2.6, base broadly cuneate, apex acuminate, acumen up to 10 mm long, rounded, upper and lower surface glabrous or thinly sericeous, midrib raised above, veins flat or slightly sunken above, slightly raised below, 7–14 per side, 3.5–10 mm apart, not reaching the margin but curving towards the apex, venation reticulate; lateral ones elliptic to narrowly elliptic, 3–7.2 x 1.5–2.7 cm, length/width ratio 2–2.6, base broadly cuneate to rounded, apex acuminate, acumen 5–7 mm long, rounded, above and below glabrous or thinly sericeous, not glaucous; pulvinus 1.5–3 mm long. Inflorescences axillary or terminal, pseudoracemes/pseudopanicles, 6.5–20 cm long, striate, (thinly) sericeous, glabrescent; peduncle 0.5–2 cm long, striate, (thinly) sericeous, glabrescent; lateral branches up to 11 cm long. Bracts subtending brachyblasts ovate to triangular, 0.6–1 x 0.4–0.8 mm, outside pubescent, inside glabrous. Brachyblasts club-shaped to elongate cylindrical, 2–13 mm long, with 3–8 flowers, sometimes disappearing near the top of the inflorescence and then flowers solitary. Bracts subtending flowers ovate with acute apex, 0.4–0.7 x 0.3–0.4 mm, outside pubescent, inside glabrous. Pedicels 2–5 mm long, sericeous. Bracteoles at the top of the pedicels, ovate, ca. 0.6 x 0.4 mm, outside pubescent, inside glabrous. Calyx maroonish, cup-shaped, 2–3 mm high, outside thinly sericeous, inside glabrous or sericeous along the margin, tube 2–2.5 mm high; upper lip with 2 short lobes, 0.2–0.3 x 2–2.5 mm; lateral and lower lobes shortly triangular, ca. 0.5 x 1.5 mm, apex obtuse or sometimes rounded. Flowers slightly fragrant. Corolla white with pinkish hue. Standard: claw 0.7–1 mm long; blade orbicular 6–7 x ca. 6 mm, apex emarginate, without auricles or basal callosities, both sides glabrous. Wings usually curved backward; claw ca. 3 mm long; blade narrowly elliptic, 7–8 x 0.7–1 mm, apex rounded, auricle ca. 1 mm long, both sides glabrous. Keel petals: claw ca. 2 mm long; blade boat-shaped, 7–7.5 x 2–2.5 mm, apex rounded, both sides glabrous, lateral pocket up to 1.5 mm long or sometime indistinct, auricle 0.8–1 mm long. Stamens monadelphous, with basal fenestrae, 10–12 mm long, free part of filaments 1.5–2 mm long, glabrous; anthers ca. 0.5 x 0.2 mm, glabrous. Disc annular, 0.2–0.3 mm high. Ovary 6.5–7 mm long, hairy, stipe indistinct; style 5–6 mm long, hairy at base; ovules 4 or 5. Pods straplike or sometime elliptic, 5–12 x 1.5–3 cm, thin, glabrescent, with wings along both sutures, upper wing 4–7 mm wide, lower wing 1–3 mm wide; seed chamber hardly visible. Seeds 1 or 2 per pod, ellipsoid, flat, ca. 8 x 19 x 1–2 mm; hilum central, 1–4 mm long.