THAI FOR. BULL. (BOT.) 33: 21–31. 2005. The genus Trigonostemon (Euphorbiaceae) in Thailand

leucanthus from China is placed in synonymy of T. albiflorus. T. heterophylla is recorded from Thailand for the first time. A key to the species, ecological data and geographical distributions are provided. Lectotypes for T. kerrii and T. quocensis are selected. Trigonostemon is a crotonoid genus of Euphorbiaceae sensu stricto. The genus comprises some 50 species and is distributed from India to northern Australia and mainly restricted to Southeast Asia. The first and last complete revision of the genus in Thailand was made by Airy Shaw in 1972 with 13 recorded species. He also pointed out that B. Sangkhachand 531, a specimen from Chanthaburi province might be a new species. Trigonostemon capillipes was thought to have unisexual inflorescence. In fact, the inflorescence always bears both staminate and pistillate flowers, with the female ones always developing before the males. During the preparation of the treatment of Trigonostemon for the Flora of Thailand, 14 species are enumerated, including T. heterophylla, a species previously known only from Yunnan, China and Laos. T. leucanthus from China is reduced to a synonym of T. albiflorus. Trigonostemon is a difficult genus to recognise because of its highly variabl