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U.S. Forest Service

Plant of the Week

No USDA PLANTS Database range map is available. Related, see Astragalus molybdenus on USDA Plants.

Schultz’s Milk-vetch (Astragalus molybdenus var. schultziorum) Astragalus molybdenus var. schultziorum. Photo by Charmaine Delmatier.

Open rocky area in sagebrush steppe. Astragalus molybdenus var. schultziorum habitat. Photo by Charmaine Delmatier.

Schultz’s Milk-vetch (Astragalus molybdenus var. schultziorum)

By Charmaine Delmatier (2014)

Schultz’s milkvetch (Astragalus molybdenus var. shultziorum) is a low, loosely-matted perennial with short stems, a slender taproot, and is a member of the legume family (Fabaceae). The small cream to lavender pea-like flowers are only 10 to 12 millimeters long and arranged individually along the main axis with the youngest flowers at the terminal end. The keel is sharply recurved and the banner has an obvious display of lilac veins. The alternate mostly-pubescent leaves can be as long 8 centimeters, but two-thirds of the leaf is buried or subterranean with the aerial tips prostrate to ascending. The smaller 17 to 25 leaflets are usually crowded, somewhat hairy, and are 2 to 10 millimeters long.

In Wyoming, Shultz’s milk-vetch is locally abundant in the northwest mountains near or above tree line in the Salt River, Teton, and Wyoming Ranges up to 11,500 feet. In Idaho, it is restricted to the southeast portion of the state. This is the extent of its range and it is considered a rarer but not endangered plant species of the Rocky Mountains. Usually you can find it in open somewhat gravelly gentle slopes.

Astragalus is a larger genus with approximately 3,000 herbs and small shrubs worldwide with over 350 species and many varieties in North America. Although referred to as a milk-vetch, the true vetches (Vicia), although having similar flowers, are usually 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.

A common question is how to tell the difference between Oxytropis and Astragalus. There is a quick field characteristic that can usually be seen 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 exciting legumes.

The taxonomic status of Shultz’s milk-vetch, also known as Astragalus shultziorum, has periodically been under review and continues to be examined; but for now, it is recognized as a rare alpine milk-vetch endemic to the high altitudes of the Rocky Mountains. It is always a treat to be walking along on an invigorating hike and notice this humble feathery alpine Astragalus growing quite independently at your feet.

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