3. Mitragyna rotundifolia (Roxburgh) Kuntze, Revis. Gen. Pl. 1: 289. 1891.
帽蕊木 mao rui mu
Nauclea rotundifolia Roxburgh, Fl. Ind. 2: 124. 1824; Mitragyna brunonis (Wallich ex G. Don) Craib; N. brunonis Wallich ex G. Don.
Trees, perhaps deciduous, to 30 m tall; branches angled to subterete, glabrous to glabrescent. Petiole 15-60 mm, glabrous to densely pilosulous; leaf blade drying papery, suborbicular to broadly elliptic or ovate, 9-25 × 6-20 cm (to 75 cm on seedlings and sprouts), adaxially glabrous to puberulent, abaxially sparsely to densely pilosulous or tomentulose, base rounded to cordate, apex rounded to obtuse; secondary veins 5-7 pairs, spreading, sometimes with pilosulous domatia in abaxial axils; stipules elliptic-oblong to ovate, 13-50 × 5-30 mm, pilosulous, keeled, apex obtuse to rounded. Inflorescences densely puberulent to pilosulous; peduncles 1-3 mm (i.e., portion above articulation of subtending leaves but not including internode below node bearing inflorescence); flowering heads 1-5, 7-10 mm in diam. across calyces, 15-20 mm in diam. across corollas; bracteoles linear-spatulate, 1-1.5 mm, glabrous or sparsely pubescent. Calyx glabrous; ovary portion 1.5-3 mm; limb ca. 0.5 mm, subtruncate to lobed for ca. 1/2; lobes triangular, obtuse. Corolla yellowish white, outside glabrous, densely hairy inside; tube 2-3 mm; lobes narrowly oblanceolate, 4-5 mm, acute. Fruiting heads 10-16 mm in diam. Capsules 3-5 mm, weakly ridged, with persistent calyx thickened; seeds ca. 1 mm. Fl. [Aug-Nov], fr. Sep, Dec.
Dense forests; ca. 1000 m. S Yunnan [Bangladesh, India, Laos, Myanmar, Thailand].
This species was illustrated by Ridsdale (Blumea 24: 66, f. 8. 1978). Puff et al. (Rubiaceae of Thailand, 46. 2005) noted that in Thailand this species is most often found in deciduous vegetation and is common in secondary vegetation.