(Dioscorides, Greek naturalist of the first or second century of the Christian era). Dios-coreacese. Twining herbs from tuberous or thickened rootstocks, grown as arbor vines or under glass for the foliage, and also for the edible rhizomes and aerial tubers.

Type genus of a small family (of about 9 genera) allied to Liliaceas. It contains more than 200 widely dispersed and confused species, most of them native to tropical regions. stems herbaceous and twining or long-procumbent, usually from a large tuberous root, and sometimes bearing tubers in the axils: leaves broad, ribbed and netted-veined, petiolate, alternate or opposite, sometimes compound: flowers dioecious, small; calyx 6-parted; anthers 6; styles 3; ovary 3-loculed and calyx adherent to it: fruit a 3-winged caps.; seeds winged. - The great subterranean tubers of some species are eaten in the manner of potatoes. Some of the kinds have handsome colored foliage and are good glasshouse subjects. Numbers of species are more or less cult, in different warm countries (see, for example, Paillieux & Bois, "Le Potager d'un Curieux," and for Japanese species Georgeson, A.G. 13:80); but it is not known that many of them have appeared in the U. S. The tuber-bearing species need to be worked over thoroughly from living plants.

For an inquiry into the prehistoric cult, of dioscoreas in Amer., see Gray & Trumbull, Amer. Journ. Sci. 25:250.

All the species are of very easy cultivation from seeds or tubers or cuttings. The tubers keep a long time, like potatoes.

A. stems strongly winged.

Alata

Linn. Fig. 1269. stem 4-winged or angular: leaves opposite, cordate-oblong, or cordate-ovate, with a deep, basal sinus, glabrous, devoid of pellucid dots, 7-nerved (sometimes 9-nerved), with the outer pair united: staminate spikes compound, special ones whorled, short, flexuose; pistillate spikes simple; flowers distant, anthers subglobose, about as long as the filament: caps, leathery, elliptical. India and the South Sea Isls. - Widely cult, in the tropics under many vernacular names. Tubers reach a length of 6-8 ft., and sometimes weigh 100 lbs.; edible. The roots continue to grow for years. Variable.

aa. stems terete (cylindrical).

B. Leaves plain green.

Batatas, Decne

(D. divaricata, Auth., not Blanco). Yam. Chinese Yam. Chinese Potato. Cinnamon-Vine. Tall climbing (10-30 ft.), the leaves 7-9-ribbed, cordate-ovate and shining, short-petioled, bearing small clusters of cinnamon-scented white flowers in the axils: root-tubers deep in the ground, 2-3 ft. long, usually larger at the lower end. Philippines. F.S. 10:971. R.H. 1854, pp. 247, 451, 452. - This is often grown in the tropics for its edible tubers, which, however, are difficult to dig. In this country the word yam is commonly applied to a tribe of sweet potatoes (see Sweet Potato). The yam is hardy. The root will remain in the ground over winter in New York, and send up handsome tall twining shoots in the spring. The plant bears little tubers in the leaf - axils, and these are usually planted to produce the cinnamon vine; but it is not until the second year that plants grown from these tubercles produce the large or full-grown yams. A form with short and potato-like tubers is D. Decaisneana, Carr. (R.H. 1865:110). - A vine widely cult, since 1910 under the name air potato" or "giant yam vine" has large potato-shaped bitter tubers. Its identity is in doubt. It is not D. divaricata, under which name it was introduced from Hawaii, nor D. bulbifera, which has angular and edible aerial tubers.

In order to distinguish it from the latter, it has recently been called the 'Hawaiian bitter yam." The yampi is apparently a form of D. alata. This and other forms of this species are grown in Fla. and La., for the excellent edible tubers, which compare favorably with the potato.

Dioscorea alata, showing foliage ( X 1/3) and a small tuber.

Fig. 1269. Dioscorea alata, showing foliage ( X 1/3) and a small tuber.

Air potato.   Aerial tuber of Dioscorea bulbifera. (X 1/4)

Fig. 1270. Air potato. - Aerial tuber of Dioscorea bulbifera. (X 1/4)

Bulbifera

Linn. Air Potato. Fig. 1270. Tall-climbing: leaves alternate, cordate-ovate and cuspidate, 7-9-nerved, the stalks longer than the blade: flowers in long, lax, drooping, axillary racemes. tropical Asia. G.C. III. 52:313. - Somewhat cultivated S. as an oddity and for the very large angular axillary tubers (which vary greatly in size and shape). These tubers sometimes weigh several pounds. They are palatable and potato-like in flavor. The root-tubers are usually small or even none.

bb. Leaves variously marked and colored, at least beneath (greenhouse "foliage plants").

Discolor

Hort. Leaves large, cordate-ovate, cuspidate, with several shades of green, white-banded along the midrib and purplish beneath: flowers greenish and inconspicuous: root tuberous. S. Amer. Lowe 54. F.W. 1877:353. - Useful for the conservatory. Suggestive of Cissus discolor.

Multicolor

Lind. & Andre\ Probably only a form of the last: leaves variously marked and blotched and veined with silvery white, red, green and salmon. S. Amer. I.H. 18:53. - Very decorative glasshouse plant of several well-marked forms (some of them under Latin names).

D. villosa, Linn., a native dioscorea, is offered. Bartlett has recently worked over .the species native to the U. S. (Bull. 189, Bur. PI. Ind., U. S. Dept. of Agric, 1910) and has recognized 5 species in the material formerly passing as D. villosa; and the name villosa itself he finds to be untenable because of the confusion attending it (a similar case lies with D. sativa, Linn., a name applied to oriental species). The 5 species are as follows: D. quaternata, Gmel. Rhizomes stout, 2/5in. diam., straight or forked, with few or no lateral branches: stems 3-8 ft. long, rigid and erect at base but requiring support above: leaves mostly 5 and 6 at a node, alternate above, cordate, repand, green on both sides, glabrous: staminate flowers panicled, the clusters solitary in the axils; pistillate flowers few in the cluster: fruit variable, 2/5-l 1/5 in. long. Woods and banks, N. C. to Fla., La., Mo. and Ark. - D. glauca, Muhl. Rhizomes 2/5in. or more diam., often forked and with many short lateral branches (the source of the drug "dioscorea"): stem 3-10 ft. long, rigid and erect at base but requiring support above: leaves in whorls of 5-7, the upper ones alternate, larger than in D. quaternata and less or not at all repand glabrous or hirtellous, glaucous at maturity: staminate inn. solitary in all axils, paniculate; pistillate infloresence few-flowered: fruit to 1 1/4 in. long.

Pa. southward along the mts. to S. C. and west to E. Mo. - D. paniculata, Michx. Rhizomes long and slender, simple or rarely forked, less than 2/5in. diam., with a few short thinner laterals: stem 3-14 ft., flexuose, glabrous: leaves all alternate or nearly so, pubescent beneath: staminate infloresence solitary in the upper axils; pistillate infloresence densely many-fruited: fruit less than 1 in. variety glabrifolia, Bartlett, has glabrous leaves Mass. to Minn., south to Texas in the middle region. - D. hirticaulis, Bartlett. Rhizome less than 2/5in. diam., simple or rarely forked, nearly striaght, with short thin laterals: stem 3-10 ft., weak and flexuose, pubescent: leaves all alternate (except perhaps at lowest node), grayish pubescent: staminate infloresence solitary in upper axils, the upper ones paniculate; pistillate infloresence with 1-4 fruits, which are nearly 1 in. long. Carolinas and Ga. - D. floridana, Bartlett. Rhizomes undescribed: stem flexuose and twining: leaves alternate, wholly glabrous, green above and paler beneath: staminate infloresence paniculate, in the upper axils and also terminal; pistillate infloresence solitary, 5-7-flowered: fruit similar to those of D. paniculata, nearly 1 in. long, S. C. to Fla.

Of the many names appearing in horticultural literature, the following are recent: D. argyraea, Hort. Leaves with silver-gray angular patches along the main nerves. Colombia. Probably one of the D. discolor-multicolor group. - D. bicolor, Hort. Greenhouse climber, with ovate and cordate leaves, variegated above and deep purple beneath. G.W. 13, p. 254. Perhaps a garden form of some species, although there is a D. bicolor, Prain & Burkill described in a

Bengal Journal

D. Fargesii, Franch. Twining, with spherical aerial tubers: leaves of 3-5 parts or leaflets, ternate or digitate, the parts oval or oval-lanceolate, more or less acuminate: female flowers in a very long cluster, sessile, subtended by lanceolate bracts; female flower oblong, with 6 short segments: subterranean tuber globular, said to be edible; plant produces aerial tubers. W. China. R.H. 1900, p. 685. - D. globosa, Roxbg. Cult, by Hindoos: tubers large, round and white: stems 6-winged, prickly toward the root: leaves sagittate-cordate, ensiform, 5-7-nerved, the long petiole 5-winged: staminate infloresence long-pendulous and compound, and verticillate; pistillate infloresence simple and erect in the axils, few-flowered India. This name is listed in Eu. - D. illustrata, Hort., appears in European lists: leaves satiny green with a central band of gray, transverse lines of white, and gray patches, under surface purple. Brazil. Probably one of the D. discolor group. - D. japonica, Thunb. stem slender, climbing 10-12 ft.: leaves ovate with tapering apex and deeply cordate base, with some of the axils bearing small oblong tubers or bulbels: pistillate flowers small, white, racemose near the top of the plant: fruit triangular, winged: root 3 - 4 ft. long, 1-2 in. diam., often branched.

Japan. Cult, forms have thicker and more condensed roots, and are eaten after the manner of potatoes. Offered abroad.' - D. macroura, Harms. Leaves simple, alternate, glabrous, stalked, cordate-orbicular, 1 ft. each way, undulate, with an apical cusp 1 1/2 - 2 in. long: male flowers in a large panicle, the racemes reaching 2 ft., the fertile stamens 6 and very short. Upper Guinea (tropical Africa). - D. retusa, Mast. stems slender, much twining, finely pubescent: leaves alternate, compound; leaflets 5, stalked obovate, retuse, to 2 in. long, green and glabrous: male flowers few, in short-peduncled racemes; perianth-segments oblong and connivent; fertile stamens 3 and staminodea 3. S. Africa G.C. 1870:1149. G.Z. 22, p. 242. L H B