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Field Milk-vetch Astragalus agrestis


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Field Milk-vetch - flower
credit: Matt Lavin/CCSA

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Alternate name: Cock's-head

Family: Fabaceae, Pea view all from this family

Description A soft green plant tending to grow in patches, with weak stems often leaning on other vegetation, and pink to lavender or purple pea flowers crowded in short heads.
Habit: native perennial herb; stems smooth or gray-hairy, slender but sturdy; from woody caudex.
Height: to 15 in (38 cm)
Leaf: alternate, odd-pinnate, to 4 in (10 cm) long; 9-25 leaflets, oblong to ovate, tips often notched, to 0.75 in (2 cm) long.
Flower: purple or pink-tinted to nearly white, sweet pea-like, 0.5-1 in (12-25 mm) long; in crowded, round to oval cluster, to 1.5 in (38 mm) tall and wide, up to 50 flowerheads, on stalk from leaf axil.
Fruit: oval pod, held upright, 3-sided, grooved on bottom side, dark shell, white-fuzzy, 0.5 (1 cm) long; dries to a papery texture.

Warning Although this species has not been reported as poisonous, all plants in the genus Astragalus are potentially toxic to humans and animals if ingested, causing a disorder called locoism. The milk from an animal that has ingested Astragalus plants may also be toxic. Sensitivity to a toxin varies with a personís age, weight, physical condition, and individual susceptibility. Children are most vulnerable because of their curiosity and small size. Toxicity can vary in a plant according to season, the plantís different parts, and its stage of growth; and plants can absorb toxic substances, such as herbicides, pesticides, and pollutants from the water, air, and soil.

Flower May to August.

Habitat Moist to dry: grasslands, moist meadows, stream banks, woodland clearnings, prairies, cool brushy slopes, pastures, roadsides; to treeline.

Range Native to North America; in Canada, from Quebec west and north to the Yukon; south to California, southern Utah, central New Mexico, Nebraska and Illinois; not reported in Arizona or Wisconsin; also in Asia.

Discussion Also called purple milkvetch, purple loco. This plant is representative of many of the low Astragalus with purplish or pink flowers; the hundreds of species in the West are difficult to identify. The seedpod is often key to successful identification within this genus. This species differs from the rest of the genus by its united stipules and its large flowers that are 0.75-1 in (19-25 mm) long and crowded into ovoid heads.

Poisonous species of Astragalus and Oxytropis are known as locoweeds.