Plants shrubby, twining, arising from the tuberous rhizomes, with broad net-veined leaves. Flowers dioecious, regular, hexandrous, tube adherent, limb 6-partcd. Ovary 3-celled, 3 to 6-ovuled, 3-styled. Stamens 6, perigynous. Fruit a capsule 3 or
(by abortion) 1-celled, or a berry. Seeds compressed, albuminous.
Genera 7, species 150. - The only remarkable or useful product of this order is Yams, an important article of food in all tropical countries. They are the large, mucilaginous, sweetish tubers of Dioscorea sativa, etc.
8. DIOSCO'REA, L. Yam Root. (In honor of Pedaeius Dioscoridcs, a Greek physician and florist of about the reign of Nero.) Flowers
; styles of the fertile flowers 3; cells of the capsule 2-seeded; seeds menibranaceously margined. - Slender, shrubby climbers, twining with the sun. Lvs. simple and palmately veined or palmately divided. Fls. green, inconspicuous, in axillary spikes or panicles.
1 D. villosa L. Wild Yam. Lvs. broad-ovate, cordate, acuminate, 9 - 11-veined, the margin entire or wavy, lower surface downy or glabrous, never villous; upper surface glabrous; petioles elongated, the lowest somewhat verticillate in 4s, the next subopposite, the middle and upper alternate; plant with the spikes paniculate, with the spikes simple. - A delicate twining vine, in thickets and hedges, U. S. and Can., rare in N. Eng. Stem woolly, reddish-brown, 1 - 2 diam., 5 - 10 - 15f long, running over bushes and fences. Leaves 2 - 4' long, 3/4 as wide, distinctly cordate and acuminate. Petioles 2 - 4' long. Peduncles axillary. Ovaries at first elliptic, finally almost as broad as long. June, July. (D. quarternata Ph.)
2 D. sativa L. Yam. Lvs. alternate, roundish-ovate, long-cuspidate, sinuate-cordate, glabrous, 9 to 13-nerved, outer nerves bifid, transverse veins simple; st. terete, smooth; spikes densely paniculate; spikes aggregate. Var. acu-leata, stems aculeate. - Native of E. India. This species, with its varieties, is understood to be that which is known as the Sweet Yam, cultivated in Ga. and. Fla., and all tropical countries, on account of its sweet and nutritious tubers. ‡