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Two-Grooved Milkvetch, Two-Grooved Poisonvetch

[Astragalus bisulcatus (Hook.) A. Gray]

Fabaceae (Legume Family)

Mature flowering plant, with fruit pods ▼▲

flowers ▼▲

flowers ▼▲

stem with fruit, and close-up of fruit pods below ▼▲

post-flowering plant loaded with pods

 

Two-Groove Milkvetch (Two-Groove Poisonvetch) is a simple, perennial native to the central and northern prairies and rangeland, particularly alkaline or high-selenium soils.  More plants will be found in disturbed or over-grazed areas in these regions, as well. 

The entire plant (not just flowers) has a unique, characteristic, strong musky odor (similar to alkali poisonvetch) that is evident when they are nearby.  The plant tends to have an upright-ascending branching pattern, with several branches arising from a simple perennial tap root.  Stems may be green or reddish, with hairy, pinnately-compound leaves with oval leaflets.  They have upright racemes of showy pinkish-purple to rose-purple flowers in late spring to early summer, followed by slender, grooved pods, with two-grooves along the midveins (hence their name).

Two-groove milkvetch appears very similar to alkali poisonvetch, and can be distinguished by the deeply grooved pods (in two-groove milkvetch) and different stipule and sepal characteristics.  Alkali poisonvetch will tend to have white to pale-purple flowers, while two-groove milkvetch will usually have purplish or rose-purple flowers, but there is overlap in flower color for both species.

Consumption of two-groove milkvetch can cause selenium toxicity in grazing animals.  This plant usually will not be grazed if more desirable vegetation is available.   

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