Wang Jiang Nan Zi

Senna occidentalis, coffee senna, is a robust annual to short-lived perennial subshrub of the Fabaceae family (Caesalpinioideae), native to the American tropics and naturalized throughout warm regions worldwide, including southern China. The plant grows erect to about one to two meters, with smooth green to purplish stems and alternate, even-pinnate compound leaves bearing four to six pairs of ovate-lanceolate leaflets that emit a fetid odor when crushed. Bright yellow five-petalled flowers are borne in short axillary racemes, producing slender flattened curved pods up to twelve centimeters long. The pods contain numerous flat, dull-brown seeds arranged transversely; these seeds, sometimes roasted as a coffee substitute, are the principal medicinal part used in TCM and have a hard, dark seedcoat that requires processing.