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U.S. Forest Service


Plant of the Week

Hyattville Milkvetch in flower and fruit from the northwest slope of Cedar Mountain, Big Horn County, Wyoming, by Charmaine Delmatier, 22 June 1993.Hyattville Milkvetch in flower and fruit from the northwest slope of Cedar Mountain, Big Horn County, Wyoming, by Charmaine Delmatier, 22 June 1993.

Hyattville Milkvetch habitat.Hyattville Milkvetch habitat, by Charmaine Delmatier.

Hyattville Milkvetch (Astragalus jejunus var. articulatus)

By Charmaine Delmatier (2014)

First discovered in 1979 by Ronald L. Hartman, Ann Odasz, and Robert Dorn independently but simultaneously, Hyattville milkvetch (Astragalus jejunus var. articulatus) is a loosely multi-stemmed perennial from the pea or legume family, Fabaceae. Its entire global distribution is restricted to the northcentral region of Wyoming, specifically on the eastern rim of the Bighorn Basin and western foothills of the Bighorn Range near the small town of Hyattville. With such an important distinction, it is located in a more common habitat amidst rolling hills of Wyoming big sagebrush and mixed grasslands. There are sporadic Utah juniper woodlands (Juniperus osteosperma) and various shrub communities dotting the landscape, and in the openings exposing the red soils, you will find Hyattville milkvetch growing along with other small cushion-like plants. The red soils are littered with whiter sandstone fragments originating from the Goose Egg and Chugwater formations (Fertig and Welp 2001).

Its small flowers vary from white to yellow and are often tinged with lavender. The larger inflated fruits are more obvious than the flowers and mottled as the markings of a leopard. The leaves and leaflets are simple and the margins smooth. Each leaf is pinnately divided with 17-25 narrow leaflets which are attached opposite to each other along the leaf’s rachis. The leaflets are no longer than 5 mm and the flowers barely reach 12 mm. But it is easily visible against the reddish soils from which it grows.

According to the Jepson Flora of California, the legume family, Fabaceae, has 730 genera and 19,400 species worldwide. Of those genera, Astragalus is a larger genus with approximately 3,000 herbs and small shrubs with over 350 species, of which many of those varieties occur in North America. Although referred to as a milkvetch; the true vetches (Vicia), have similar flowers, but are vine-like and often have a terminal stringy tendril.

Astragalus is also referred to as a locoweed, however, there are two genera loosely commonly referred to as locoweed, Astragalus and Oxytropis. According to Stanley L. Welsh, Michael Ralphs, and Bryan Stegelmeier in various separate publications, of the 600 toxic locoweeds worldwide, approximately 21 species occur in the United States. Some are more harmful to grazing undulates, specifically domestic cattle and horses. Locoweeds produce a potentially toxic alkaloid, swainsonine, that inhibits the production of crucial enzymes which in turn trigger an unhealthy reservoir of only partially metabolized sugars and disrupts protein synthesis. Grazing animals will lose their appetite, become reluctant to move, and eventually suffer from severe weight loss.

One of the more common questions asked is how to tell the difference between Oxytropis and Astragalus. There is a quick field characteristic you can usually see with the naked eye, but sometimes it will require a hand lens. If the keel on the flower is narrowed to a slender beak, then it is Oxytropis, but additional field characteristics will further narrow down specific identifications for many other common and rare legumes.

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