Description from Flora of China
Paradina Pierre ex Pitard; Stephegyne Korthals.
Trees, unarmed; buds flattened, with stipules erect and pressed together. Raphides absent. Leaves opposite, sometimes with domatia; stipules caducous, interpetiolar, generally ovate to obovate, sometimes keeled, entire, often well developed. Inflorescences terminal on main stems and axillary branches and often accompanied by reduced, petaloid, and/or bracteate leaves, capitate with globose heads in fascicles, cymes, umbels, or thyrses, sessile to shortly pedunculate, bracteate; bracteoles spatulate to obpyramidal. Flowers sessile, bisexual, monomorphic. Calyx limb truncate to 5-lobed. Corolla cream to yellow-green, funnelform or narrowly salverform, inside glabrous to variously pubescent; lobes 5, valvate in bud. Stamens 5, inserted near corolla throat, exserted or included; filaments short; anthers basifixed, partially to fully exserted. Ovary 2-celled, ovules numerous in each cell on fleshy, pendulous, axile placentas attached in upper third of septum; stigma clavate to mitriform (i.e., upside-down cupular), exserted. Fruit capsular, obovoid to ellipsoid, septicidally then loculicidally dehiscent, cartilaginous to woody, with calyx limb persistent or deciduous; seeds numerous, small, somewhat flattened, fusiform to lanceolate, shortly winged at both ends with basal wing sometimes bifid or notched.
Ridsdale reviewed this genus in detail (Blumea 24: 46-68. 1978) and excluded the African species. H. H. Hsue and H. Wu (in FRPS 71(1): 245. 1999) reported only Mitragyna rotundifolia from China; Ridsdale (loc. cit.: 65) reported only M. diversifolia from China; and Wu (Acta Phytotax. Sin. 6: 293. 1957) reported a third species, M. hirsuta, in a report that has been overlooked. Several other species of Mitragyna are found widely in Thailand and Myanmar, as well as cultivated for lumber, and should be expected in China (in particular, see comments under M. diversifolia). The leaves of M. speciosa (Korthals) Haviland are the source of kratom and used for tea, chewing, smoking, and as medicine in Thailand and Malaysia; the main active ingredient here is the alkaloid mitragynine, known only from this species and said to be stimulating at low doses but narcotic at high doses.
About seven species: one species in Africa, six species in Asia and Malesia; three species in China.
(Authors: Chen Tao (陈涛); Charlotte M. Taylor)