Flower:

One-sided raceme of 10 to 40 pea-shaped flowers on stalks arising from leaf axils in the upper stem. Flowers are ½ to ¾ inch long, the upper petal (the standard) flaring upward, lateral wings below it oval, extending outward. The erect part of the standard (the banner) is about half as long as the part that forms the floral tube (the claw) and is typically pink to deep purple or blue-violet with paler lateral wings, though sometimes all flowers in a cluster are solid white.

The calyx holding the flower has 5 narrow lobes, the upper lobes narrowly triangular and shorter than the calyx tube, the lower lobes much longer than the upper and may be longer than the calyx tube. The base of the calyx is swollen, noticeably extending past where it attaches to the short flower stalk. Flower stalks and the calyx are both variously covered in spreading hairs.

Leaves and stems:

Leaves are compound with 8 to 12 pairs of leaflets, and a branched tendril at the end that entwines surrounding vegetation for support. Leaves can be up to 10 inches long and 2 inches wide but 6 inches or less is typical. Leaflets are about 1 inch long and ¼ inch wide, toothless, hairy, generally elliptical.

At the base of the leaf stalk is a pair of narrow, leafy appendages (stipules) that are ¼ to 1/3 inch long and densely hairy. Stems are vining, multi-branched and sprawling, with distinct ridges and covered in spreading hairs.

Fruit:

Fruit is a flattened pea pod up to 2 inches long, containing several round seeds.

Notes:

A historical forage introduction, this aggressive legume has spread widely in east central Minnesota and is a common purple flower in the landscape along roadsides and fields, forming dense mats of tangled stems. Walking through a patch of it can be like trudging through a jungle. As with any flower it has some aesthetic value but for the human mind only, it is of marginal forage need to larger herbivores and provides poor wildlife habitat with little or no insect productivity while spreading in higher grade native habitats, particularly in restoration areas. It is likely under-reported in Minnesota.

It is often confused with Tufted Vetch (Vicia cracca), which usually has short, appressed hairs on stems, stalks and calyces where Hairy Vetch is usually more densely covered in longer, spreading hairs, but hairs alone may not lead to a positive ID. A post on iNaturalist details differences in the flowers that can further distinguish them (see also the image below). In a nutshell:

• On V. cracca, the banner is about as long as the claw, where on V. villosa the banner is about half as long as the claw so flowers look more elongated. This is pretty obvious and may even be detected from some distance.
• On V. cracca, the calyx base is not swollen or is only slightly so, where on V. villosa the base is distinctly swollen so it noticeably bulges beyond where the flower stalk is attached.
• On V. cracca, the calyx lobes are all triangular and relatively short, where on V. villosa the lobes are narrow and elongated, especially the lower lobes.

Vicia cracca is also perennial where V. villosa is annual, biennial or short-lived perennial. V. cracca is more common in northern Minnesota and V. villosa is more common in the central and southern counties, but reports at EDDMapS and iNaturalist have their ranges starting to overlap, with several reports of V. cracca in or near the Twin Cities Metro area; it is possible some of those reports are mis-IDs due to the ease of mistaking one for the other. In any case, both are weedy and can create dense, tangled mats.

USDA reports 4 subspecies, 2 of which are relatively common in the US but only one, subsp. villosa (described above), is known to be in Minnesota. Subsp. varia (a.k.a. V. dasycarpa) has been recorded in Wisconsin and is likely here as well; it is much like subsp. villosa in flower characteristics but hairless to sparsely hairy with somewhat shorter calyx lobes.