巴豆 ba dou

Alchornea vaniotii H. Léveillé; Croton birmanicus Müller Argoviensis; C. himalaicus D. G. Long; C. xiaopadou H. S. Kiu.

Treelets up to 7 m tall; indumentum of stellate hairs; young branches green, sparsely stellate-hairy, glabrous at maturity. Stipules subulate, 1.5-4 mm, caducous; petiole 2.5-6 cm, subglabrous; leaf blade ovate, ovate-elliptic, or ovate-lanceolate, 5-15 × 2-7 cm, papery, glabrous or glabrescent, yellowish to brownish when dry, base cuneate or broadly so, rounded, rarely slightly cordate, with discoid glands, margins serrulate or subentire, apex acute or acuminate, sometimes long acuminate or caudate-acuminate; basal veins 3(-5), lateral veins 3 or 4. Racemes terminal, 8-20 cm; bracts subulate, ca. 2 mm. Male flowers: bud subglobose, sparsely stellate-hairy or glabrescent. Female flowers: sepals oblong-lanceolate, ca. 2.5 mm, glabrescent; ovary densely stellate-hairy; styles bipartite. Capsules ellipsoidal, oblong-ovoid, or subglobose, 1-2 × 1-2 cm, sparsely stellate-hairy or glabrescent. Seeds elliptic or oblong-ovate, 8-12 × 6-7 mm, gray-brown. Fl. Jan-Jul, fr. May-Sep.

Montane sparse forests, limestone shrublands; 300-700 m. Fujian, Guangdong, Guangxi, Guizhou, Hainan, Jiangsu, Jiangxi, Sichuan, Taiwan, Yunnan, Zhejiang [Bangladesh, Bhutan, Cambodia, India, Indonesia, Japan, Malaysia, Myanmar, Nepal, Philippines, Thailand, Sri Lanka, Vietnam].

The seed oil contains crotin, tiglic and crotonic acid, and crotonoside, and is very poisonous, being a drastic purgative and often causing pustular eruptions on the skin. The seeds are used to stupefy fish. The root and leaves are used as an external medicine for rheumatalgia and also as an insecticide.

The name "Croton tiglium var. xiaopadou" (Y. T. Chang & S. Z. Huang, Wuyi Sci. J. 2: 23. 1982) was not validly published because two gatherings were indicated as types (Vienna Code, Art. 37.2). The name was later validated, at species rank, by H. S. Kiu (J. Trop. Subtrop. Bot. 6: 103. 1998).