2. Dioscorea quaternata (Walter) J.F. Gmel. (wild yam)

Pl. 88 a–c; Map 334

D. quaternata var. glauca (Muhl.) Fernald

Aerial stems from horizontal rhizomes, these 10–15 mm in diameter when fresh, contorted and with many knobs or short side-branches. Leaves in whorls of 3–9 below, becoming alternate above, 4–26 cm long, heart-shaped, the base cordate and the tip acuminate. Aerial tubers not produced. Fruits 18–26 mm long. Seeds 9–13 mm wide including the wing. 2n=36, 54, 60. April–June.

Scattered in the Ozark and Ozark Border counties (eastern U.S. west to Missouri and Texas). Mesic bottomland and upland forests, frequently on mesic, rocky slopes, thickets along creeks.

Aside from characters of the rhizomes and the lower leaves mentioned in the key to species, D. quaternata and D. villosa can be difficult to distinguish vegetatively. One useful feature best observed on fresh material is that the aerial stems of D. quaternata are round or nearly so in cross-section, whereas those of D. villosa tend to be 8–14-angled or ridged. The flowers and fruits of these species are nearly identical.