1. Dioscorea oppositifolia L. (Chinese yam, cinnamon vine)

Pl. 88 f; Map 333

D. batatas Decne.

Aerial stems from deep-seated, elongate, vertical tubers. Leaves alternate or opposite, rarely in whorls of 3, 4–14 cm long, heart-shaped to fiddle-shaped, with the basal lobes usually enlarged and deeply cordate and the tip acuminate. Small, globose, aerial tubers usually produced in the leaf axils. Fruits not produced in Missouri plants. 2n=138, 140, 142, 144. June–August.

Introduced, escaped from horticultural plantings in the southern half of the state, in the Ozark, Ozark Border, and Mississippi Lowland Divisions (native to China, widely planted and escaping from cultivation in the eastern U.S.). Mesic bottomland forests, old homesites, and disturbed roadsides.

Since its discovery in 1975 (Nelson, 1982), this species has been reported from several counties scattered through the Ozarks and the Bootheel. It escapes from ornamental plantings around old homesites, and although Missouri plants do not set fruit, the species is dispersed vegetatively by means of the edible, aerial tubers produced in the leaf axils. These are spread by water but can also be carried in dirt moved for construction projects. When established, this vigorous species can grow so thickly as to choke out the native understory and ground layer of the bottomland forests it invades.