Balloonpod Milkvetch

Within the Astragalus genus there are many hard to distinguish species. Balloonpod milkvetch (Astragalus whitneyi), because of its distinctive pods, is more readily identified. Yet with five listed varieties, four of which are found in California, identification, at least for me, remains difficult. Thus I will not attempt to go beyond the species designation.

Balloonpod milkvetch is a native perennial of mid to high elevations found on the east slopes of the Cascades and Sierra Nevada of Washington, California and Oregon and into Idaho and Nevada. Its habitat is rocky, often serpentine, soils and open talus slopes.

Assuming the form of a tuft, balloonpod milkvetch has spreading stems that point upward with the lower leaf stalks fused about the stem. The pinnately compound leaves have oblong to ovate leaflets and papery stipule sheaths (leaflike appendages at the base of the petiole or leaf stalk). The leaflets are finely hairy on the bottom side and may or may not be hairy on the upper surface.

The five cream balloonpod milkvetch flowers are the typical “pea-shape” found in members of the Pea Family (Fabaceae) and occur as a raceme on the terminal ends of the stems. In some plants the upper petals can be pinkish or purple.

Balloonpod milkvetch fruits are inflated, egg-shaped bladders that contain olive to black seeds. These somewhat transparent pods are tan and mottled red to purple. As the seeds mature the pods loose their splotches and turn a shiny golden color. When dry, the seeds rattle inside the pods. At maturity the bladders detach and drift in the wind eventually shattering and dispersing their seeds.

I brought some balloonpod milkvetch pods home to photograph the seeds. Much to my surprise there were no seeds in the pods. Instead I found small white larvae eating all the seeds. Maybe when I am more ambitious, or interested, I will research what is using balloonpod milkvetch as a host.

A whitneyi is also commonly called Whitney’s milk vetch. Josiah Dwight Whitney (1819 – 1896), a State Geologist of California, is honored by this colloquial name and the species designation. The genus, Astragalus, comes from the Greek “astragalos” meaning “ankle bone”.  Some of the seeds in the Pea Family apparently reminded someone of ankle bones.

Although I found no specific information about balloonpod milkvetch, many species of Astragalus are know to accumulate selenium which upsets the protein metabolism of animals that feed on the plants. Additionally, most Astragalus species contain a alkaloid-like substance called locine. The effects of locine are cumulative. If large amounts of the plant are eaten over several days,symptoms such as lack of coordination and muscular control coupled with unpredictable behavior when aroused occur. For this reason, many Astragalus species are known as locoweeds.

These balloon milkvetch plants were growing on rocky, disturbed soils south of Canby near where Modoc County Road 84 interscts California Highway 299E (Modoc County CA).

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3 Responses to Balloonpod Milkvetch

  1. tonytomeo says:

    I just featured a species of vetch for the Six on Saturday meme, but it is not a native. It is a common naturalized vetch, although I did not identify it.

  2. Lin Erickson says:

    Interesting plant!

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