Agylophora Necker ex Rafinesque; Ourouparia Aublet.

Woody vines or lianas, climbing by recurved, usually paired spines generally 1-2 cm. Raphides absent. Leaves opposite, usually with domatia; stipules persistent or caducous, interpetiolar, generally ovate to ligulate in outline, entire to 2-lobed, usually reflexed. Inflorescences axillary and sometimes also terminal, capitate with heads globose and 1 to several in cymes or fascicles, pedunculate, bracteate; peduncles usually articulate in middle or upper portion, often with stipuliform bracts at articulation; bracts enclosing heads sometimes caducous, involucral, stipuliform. Flowers sessile and bracteolate or pedicellate and bracteolate or ebracteolate, bisexual, monomorphic. Calyx limb 5-lobed. Corolla white to yellow, salverform or funnelform, inside glabrous or pubescent; lobes 5, imbricate in bud. Stamens 5, inserted in corolla tube near throat, exserted; filaments short; anthers dorsifixed. Ovary 2-celled, ovules numerous in each cell on axile placentas attached in upper third of septum; stigma globose or clavate, exserted. Fruiting heads globose, with fruiting pedicels when present often elongating notably. Fruit capsular, fusiform to obovoid, loculicidally dehiscent into 2 valves that usually remain attached at both ends, thinly to thickly papery or cartilaginous, with calyx limb persistent; seeds numerous, small to medium-sized, fusiform, flattened, winged with wing deeply bifid.

Ridsdale (Blumea 24: 43-46. 1978) presented an extensive consideration of the morphology, branching, and architecture of Uncaria. The characteristic hooked spines have been interpreted variously as modified plagiotropic shoots (Ridsdale, loc. cit.), peduncles that are modified into spines (e.g., Steyermark in Lasser, Fl. Venezuela 9: 32. 1974), and short shoots modified into thorns (Robbrecht, Opera Bot. Belg. 1: 1-271. 1988). By any name, these structures function to support the plants as they climb and sometimes bear a terminal inflorescence. Ridsdale (loc. cit.: 69) described the corolla lobe aestivation as valvate or thinly imbricate at their apices; other authors described them as imbricate. Uncaria was reviewed in detail for China by How (Sunyatsenia 6: 231-262. 1946), who emended the circumscriptions of several species, and then by Hsue and Wu (J. S. China Agric. Coll. 2(8): 21-32. 1981), who recognized ten species. The arrangement of the flowers and fruit, whether sessile or pedicellate, is taxonomically important; however, the pedicels usually elongate shortly before the flowers open and then continue to elongate as the fruit develop, often markedly, so the pedicel length at anthesis may be difficult to discern from inflorescences in bud.

Uncaria is considered medicinally useful, with uses ranging from general tonics to supposedly curing HIV-AIDS (e.g., K. C. Hsia & X. M. Liu, Acta Phytotax. Sin. 20: 319-320. 1982). Various parts of the plants are apparently used, with the materials generally wild-collected. Uncaria gambir (W. Hunter) Roxburgh, found from the Malay Peninsula through Borneo, is apparently both cultivated and wild-harvested as the source of gambir or gambier (Ridsdale, loc. cit.: 82; Mabberley, Mabberley’s Pl.-Book, ed. 3, 885-886. 2008), a yellowish dry resin chewed together with the betel nut and sometimes used in tanning. How (loc. cit.) noted that the Chinese drug Kou-T’eng is derived from the "hardened sterile peduncle with attached portions of the stem" of a species that is probably U. rhynchophylla.

About 34 species: 29 in tropical Asia through Australia, three in Africa and Madagascar, two in tropical America; 12 species (five endemic) in China.

(Authors: Chen Tao (陈涛); Charlotte M. Taylor)