Vicia villosa Roth (woolly vetch, winter vetch)

Pl. 411 c, d; Map 1831

Plants annual or biennial, with taproots. Stems 40–100 cm long, erect to loosely ascending, trailing, or climbing, glabrous to sparsely pubescent with short, incurved hairs or moderately to densely pubescent with conspicuous, spreading hairs. Leaves with (10)12–18(20) leaflets, the petiole absent or to 3 mm long, the tendrils branched. Stipules 5–8 mm long, lacking a glandular spot, with a narrowly triangular basal lobe, the margins otherwise entire. Leaflets 10–30 mm long, 2–6 mm wide, those of the lower leaves not strongly reduced, narrowly oblong-lanceolate to narrowly elliptic or linear, rounded to more commonly angled or tapered at the base, variously rounded to bluntly or sharply pointed at the tip, the midvein often extended as a minute, sharp point at the very tip, the surfaces glabrous or finely hairy. Inflorescences racemes, the stalk 3–9 cm long, the flowers 10–40(–60), each with a stalk 1–2 mm long. Calyces glabrous or finely hairy, often bluish- or purplish-tinged, the tube 2–3 mm long, the base strongly oblique and conspicuously pouched on 1 side, the attachment appearing lateral, the lobes 0.5–4.0 mm long, strongly unequal, the upper pair short and triangular to broadly triangular, the lowermost much longer than the upper pair, narrowly triangular to lanceolate-triangular, or more or less hairlike above a short, triangular base. Corollas (10–)12–18 mm long, blue to purple or rarely pink or white, the keel and wings sometimes lighter than the banner, the banner bent or curved upward toward the tip, strongly curved around the wings and keel. Stamens with the fused portion 9–10 mm long, the free portion 1.5–3.0 mm long. Style with a dense ring of short hairs at the base and a patch of dense short hairs on the lower side near the tip. Fruits 25–30 mm long, 7–10 mm wide, short-stalked, sometimes finely hairy when young, glabrous at maturity, straw-colored to light brown at maturity, 3–7-seeded. Seeds 3.5–5.0 mm long, dark reddish brown to greenish brown or nearly black, often with darker mottling, more or less circular in outline, not or only slightly flattened, the attachment scar not raised, dark brown, inconspicuous, extending less than 1/4 the circumference of the seed. 2n=14, 28. May–July.

Introduced, scattered south of the Missouri River, extending farther north mostly in counties along the Missouri and Mississippi Rivers (native of Europe, Asia; introduced widely in the U.S. [including Alaska], Canada, Mexico, Central America, South America, Africa). Banks of streams and rivers, edges of mesic upland forests, and rarely margins of upland prairies; also levees, fencerows, old fields, margins of crop fields, fallow fields, ditches, railroads, roadsides, and open disturbed areas.

This species is commonly planted along highways for erosion control and can become established along gravel bars when rains wash seeds or pieces of plants into drainages that cross the roads. Plants of V. villosa can form such dense, tangled mats that they smother other plant species. The species sometimes also has been planted as a green manure. It is reported to be outcrossing (Gunn, 1979).

Vicia villosa is distinguished by the densely flowered racemes of slender, mostly violet or blue flowers, the distinctly oblique and gibbous base of the calyx, narrow calyx lobes, and relatively broad fruits. Most authors divide V. villosa into two varieties or subspecies, which have sometimes been treated as separate species (Hermann, 1960; Steyermark, 1963). The two infraspecific taxa are about equally abundant in Missouri, although north of the Missouri River ssp. villosa is the variant more likely to be encountered.