Wyoming Locoweed
Oxytropis nana Nutt.
Family: Fabaceae, Pea
Genus: Oxytropis
Synonyms: Oxytropis besseyi
Other names: Bessey's pointvetch
Nomenclature: nana = a female dwarf
Nativity / Invasiveness: Montana native plant
Poisonous plant
No medicinal data

General: tufted perennial, silvery with flat hairs throughout or, as in our varieties, with spreading hairs on the calyx and pods, from a branched, woody root crown.

Leaves: basal, 2-11 cm long, odd-pinnate, the 7-21 leaflets in pairs with one at the end, 5-20 mm long. Stipules membranous, joined to the leaf stalk over half their length, only slightly or not at all joined to both sides of the stem.

Flowers: about 5 to 30 in congested, rounded clusters, the main stalks erect, 8-20 cm tall. Bracts at flower bases herbaceous, sparsely flat-long-hairy. Flowers deep reddish-purple, fading to bluish, 18-24 mm long. Calyx 10-15 mm long, sparsely to rather densely stiff-spreading-hairy, usually covering the pod until near maturity and finally ruptured, the linear-lanceolate teeth 2/3 as long as the tube. Banner erect, wings usually shallowly 2-lobed. Beak of the keel 1-1.5 mm long. June-July.

Fruits: pods, 1-2 cm long, the upper seam intruded about halfway, the beak about 5 mm long.


Gravel benches, prairies, riverbanks, and lower foothills, in most parts of MT. Also in n.w. CO and c. ID.
var. argophylla:
var. besseyi:
Poisonous Properties

Locoweed has caused a number of problems in cattle, horses, and sheep. Swainsonine, an indolizidine alkaloid, inhibits alpha-mannosidase in animal bodies, which can lead to disruption of cellular function. Locoism is a chronic disease that causes depression, incoordination, and nervousness under stress. Death can result. The cellular problems occur most readily in tissues of the nervous system. Pregnant animals often abort or give birth to young with congenital deformities. Congestive right heart disease occurs at high altitudes. The blooms and mature fruit of locoweed have higher quantities of the toxin swainsonine than do the leaves. The concentration of this toxin remains constant in leaves throughout the grazing season.

Sub taxa:

var. argophylla (Rydb.) Isely:
Flower stems 2-9 cm tall. Flower clusters closely 3- to 10-flowered. In s.w. MT and adj. ID.

var. besseyi (Rydb.) Isely:
Flower stems 10-20 cm tall. Flower clusters loosely 8- to 20-flowered. On the e. slope of the Rocky Mts. from c. MT to n.e. WY and s. Sask.

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