About Dioscorea mexicana Scheidw.
Dioscorea mexicana, commonly called Mexican yam or cabeza de negro, is a yam species belonging to the genus Dioscorea. It is a caudiciform Dioscorea that produces a dome-shaped caudex, which grows partly or completely above ground. The caudex has a thick, woody outer layer, reaching up to 3 feet (90 cm) in diameter and 8–10 inches (20 to 25 cm) in height. The caudex of D. mexicana is split into regular polygonal plates that become more protruding as the plant ages, with deep fissures separating the plates. Vigorous annual vines growing from the caudex can reach 30 feet (9 m) long before dying back each winter, and these vines bear heart-shaped leaves. The natural range of Dioscorea mexicana extends from the Mexican state of San Luis Potosí in northeastern Mexico south to Panama. This species is well known for producing diosgenin, a compound used as a precursor for synthesizing hormones such as progesterone. Russell Marker developed methods to extract and manufacture hormones from D. mexicana while working at Syntex. Later, the Mexican barbasco trade shifted its focus to Dioscorea composita instead, because this species has a higher diosgenin content.
