L.
Description
Dioscorea bulbifera, the air potato or aerial yam, is a widely distributed twining vine of the Old World tropics, native across tropical Africa and Asia and now pantropically naturalised, including invasive populations in the southern United States, the Pacific and the Neotropics. It is among the most heavily recorded yams, GBIF holding over 16,000 occurrences. In the Himalaya it grows in subtropical forest, forest margins, thickets and disturbed ground at low to middle elevations. The plant from Zhemgang in central Bhutan at 1000 m in October occupies this warm foothill zone, where its aerial tubers ripen toward the season's end.
It is a herbaceous perennial climber arising from an underground tuber, the slender stems twining to the left (sinistrorse) and bearing in the leaf axils the diagnostic rounded to angular aerial bulbils that give the plant its names and serve as its chief means of propagation. The leaves are alternate, broadly cordate-ovate with a deeply notched base and long acuminate apex, palmately veined and long-petiolate. It is dioecious: the minute flowers are borne in slender pendulous spikes, staminate clustered and pistillate more lax, with a perianth of six tepals; the fruit, where set, is a three-winged loculicidal capsule with winged seeds, though sexual reproduction is often supplanted by the prolific bulbils.
Dioscorea, the type genus of Dioscoreaceae, is a large pantropical genus of economically vital yams. D. bulbifera is enormously variable, comprising numerous cytotypes and forms; some strains are cultivated for edible tubers while others are bitter and toxic, containing the sapogenin diosgenin and the toxic principle dioscorine. Its facility for clonal spread by bulbils has made it a notorious invasive weed beyond its native range, though within the Himalaya it is a common, unremarkable component of the disturbed subtropical flora.
Author: L. · Sources: POWO (Kew), GBIF, Flora of China Vol. 24, Flora of Bhutan Vol. 3, Annotated Checklist of the Flowering Plants of Nepal, Burkill account of Asiatic Dioscoreaceae