5. Vitis riparia Michx. (riverbank grape, frost grape)

V. riparia var. praecox Engelm. ex L.H. Bailey

V. riparia var. syrticola (Fernald & Wiegand) Fernald

Pl. 581 c, d; Map 2721

Young stems circular in cross-section, glabrous or sparsely and minutely hairy at flowering time, green, gray, or brown, the nodes sometimes glaucous, not reddish-tinged. Pith interrupted at the nodes, the diaphragms 0.5–1.0 mm wide on new growth, eventually thickening to 1–2 mm wide on older branches. Older stems with the bark shredding, not appearing warty. Tendrils common, present at no more than 2 adjacent nodes (every third node lacking both a tendril and an inflorescence), 2- or 3-branched. Leaves with the petiole 1/2–2/3 as long as the blades, sparsely hairy to glabrous at flowering time. Leaf blades mostly 3–20 cm long, slightly longer than to about as long as wide, ovate to broadly ovate or nearly circular in outline, flat at maturity, mostly shallowly 3-lobed, less commonly unlobed or more deeply 3-lobed, the sinuses U-shaped or more commonly V-shaped, the lobes tapered or narrowed to a sharply pointed tip, the upper surface glabrous (occasionally sparsely and minutely hairy when young), usually not shiny. Undersurface of young leaves sparsely to moderately pubescent with minute, straight, more or or less spreading hairs along the main veins, not glaucous. Inflorescences at no more than 2 adjacent nodes, 4–12 cm long, mostly narrowly pyramid-shaped. Fruits mostly more than 25 per infructescence, 6–12 mm in diameter, the surface with lenticels absent, black, glaucous. Seeds 5–6 mm long, dark brown. 2n=38. April–June.

Scattered in eastern Missouri, becoming uncommon farther south, and absent from most of the Ozark Division (northern U.S. south to Virginia, Louisiana, and Oregon; Canada). Bottomland forests, mesic upland forests, bases and ledges of bluffs, edges of bottomland prairies, and banks of streams and rivers; also fencerows, and roadsides.

Steyermark (1963) split V. riparia into three varieties differing only in pubescence density and quantitative details of inflorescences, fruits, and seeds. Moore (1991) did not accept these varieties, which appear to represent no more than extremes in a continuum of independant character variations.