Dioscorea mexicana

Dioscorea mexicana, Mexican yam or cabeza de negro is a species of yam in the genus Dioscorea.^[1]

Mexican yam
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Monocots
Order:	Dioscoreales
Family:	Dioscoreaceae
Genus:	Dioscorea
Species:	D. mexicana
Binomial name
Dioscorea mexicana Scheidw.
Synonyms[1]
Dioscorea macrostachya Benth. Dioscorea macrophylla M.Martens & Galeotti Dioscorea deppei Schiede ex Schltdl. Dioscorea bilbergiana Kunth Dioscorea leiboldiana Kunth Dioscorea propinqua Hemsl. Testudinaria cocolmeca Procop. Dioscorea astrostigma Uline Dioscorea macrostachya var. sessiliflora Uline Dioscorea tuerckheimii R.Knuth Dioscorea anconensis R.Knuth Dioscorea deamii Matuda Dioscorea mexicana var. sessiliflora (Uline) Matuda Testudinaria macrostachya (Benth.) G.D.Rowley

Dioscorea mexicana is a caudiciform dioscorea having either a partly to completely above-ground dome-shaped caudex with a thick, woody outer layer up to 3 feet (90 cm) in diameter and 8–10 inches (20 to 25 cm) in height. The caudex of D. mexicana is divided into regular polygonal plates that become protuberant with age, and separated by deep fissures. The vigorous annual vines which may reach 30 feet (9 m) long before dying back in winter, that grow up from the caudex, bear heart-shaped leaves.^[2]

Dioscorea mexicana ranges from the state of San Luis Potosí in northeastern Mexico south to Panama.^{[3][4][5][6][7][8][9]} It is notable for its production of diosgenin, which is a precursor for the synthesis of hormones such as progesterone.^[10] Russell Marker developed the extraction and manufacture of hormones from D. mexicana at Syntex. Later the Mexican barbasco trade focused instead on Dioscorea composita instead, as this variety has a higher diosgenin content.^[11]