Oxytropis lambertii (Lambert's Locoweed)

Plant Info
Also known as: Purple Locoweed
Family:Fabaceae (Pea)
Life cycle:perennial
Habitat:sun; dry prairies and plains
Bloom season:May - June
Plant height:4 to 16 inches
Wetland Indicator Status:GP: UPL MW: FACU NCNE: FACU
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: irregular Cluster type: spike

[photo of flowers] Spike cluster up to 12 inches long on a hairy, leafless stem, with up to 25 flowers in a cluster and typically rising well above the leaves. Flowers are pea-shaped, deep pink to purple later turning blue, about ¾ inch long and stalkless. The erect upper petal (standard) is notched at the tip, sides rolled back, and has a large pale patch in the center streaked with darker lines. The 2 lateral petals fold over a keel that is abruptly tapered to a small projection (“beak”) at the tip. The calyx is 1/3 to ½ inch long, purplish, with short narrow teeth around the tip and covered in long, silky hairs. A small, hairy, leaf-like bract is at the base of the calyx.

Leaves and stems: Leaf attachment: basal Leaf type: compound

[photo of leaves] Leaves are basal in tight rosettes surrounding or near a flowering stem, mostly erect to ascending, up to about 6 inches long, compound in groups of 9 to 19 leaflets. Leaflets are stalkless, linear-oblong, 1/3 to 1 inch long and covered in long, silky hairs. At the base of each compound leaf stalk is a hairy, lance-linear appendage (stipule), up to about ½ inch long with a sharply pointed tip. Flowering stems are multiple from the base, a plant forming a clump.

Fruit: Fruit type: capsule/pod

[photo of fruit] Fruit is an erect, hairy, cylindric pod ½ to 1 inch long with the remains of the style at the tip and containing smooth, brown seeds. The pod may become smooth with age.


Of the 4 Oxytropis species ever recorded in Minnesota, this is the only one likely to be encountered in the wild. Two species—Flat Locoweed (O. campestris) and Showy Locoweed (O. splendens)—are likely extinct in the state and the fourth, Sticky Locoweed (O. viscida, or O. borealis var. viscida) is only known from a single location in Cook County on a north-facing cliff near the Canadian border. O. campestris, a Federally Threatened species, is known from a handful of locations in Wisconsin and is found along sandy lakeshores that have fluctuating water levels. O. spendens, found in the Dakotas westward, has unique compound leaves with whorled leaflets. The locoweeds (Oxytropis species) resemble the related milkvetches (Astragalus species) but are easily distinguished by the beaked keel on the flowers combined with basal leaf clumps surrounded by small stipules, where Astragalus leaves are arranged along the stems and a keel with a rounded or pointed tip but not typically beaked. There are 3 recognized varieties of O. lambertii, 2 of which have limited ranges from Texas to Utah, and var. lambertii found throughout the Great Plains and in Minnesota.

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More photos

Photos courtesy Peter M. Dziuk taken in Big Stone State Park, Big Stone County, and Glacial Lakes State Park, Pope County.


Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Diana
on: 2023-06-01 07:04:51

Found this species in Beltrami County (Bemidji) - growing amongst weeds and blooming in a highway right of way near town. Will be adding this observation to iNaturalist.

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