Photo © Robert K. Moseley
CLICK PHOTO FOR A LARGER IMAGE

Astragalus bisulcatus (Hook.) A. Gray var. bisulcatus

Two-grooved milkvetch

Fabaceae (Pea; Legume family)

General Description: A stout, erect, clump-forming, leafy, and thinly pubescent perennial herb 15-70 cm tall. The compound leaves have 15-35, more or less oblong leaflets, each between 5 and 30 mm long. The inflorescence is a dense raceme of whitish or purplish flowers. The banner is 11-17 mm long, and longer than the wings or keel petal. The calyx is 5-10 mm long, often red-purple, with thin white or black hairs, and the base swollen on one side. The pendulous, linear or narrowly oblong fruit pods have a short stipe, a thick papery texture, and are 10-20 mm long. The front face of the pod is openly grooved lengthwise along either side of the raised suture.

Illustration.

Field Identification Tips: Two-grooved milkvetch is recognized by its very leafy, clumpy habit, dense inflorescence of relatively large whitish to purplish flowers, basally pouched calyx, and pendulous, two-grooved fruit pod. Bagged plants and those drying in a plant press often give off a strong, disagreeable smell of selenium.

Photo © Robert K. Moseley
CLICK PHOTO FOR A LARGER IMAGE

Phenology: Flowers May to August.

Similar Species: Two-grooved milkvetch is most likely to be confused with other robust, leafy milkvetches having many leaflets and many, relatively large flowers. Astragalus canadensis (Canada milkvetch) is most readily distinguished by its erect, sessile, more or less leathery-textured fruit pods. Additional distinguishing characteristics include its rhizomatous root system, pick-shaped pubescence, and greenish-white or yellowish-white-colored flowers. While the pods of A. drummondii (Drummond's milkvetch) are pendulous like two-grooved milkvetch, they differ in being bluntly three-angled in shape and having a longer stipe (5-11 mm long). In addition, the flowers tend to be larger (17-25 mm) and the foliage more hairy.

Habitat: Open grasslands, badlands, gullies, roadsides, and valley bottoms. In Idaho, populations occur in relatively moist sagebrush/grassland or creek bottom habitats, sometimes in degraded condition. Associated species include Artemisia tridentata ssp. tridentata, A. tridentata ssp. wyomingensis, Rosa woodsii, Salix spp., Leymus cinereus, Pascopyrum smithii, and Poa pratensis.

Global Distribution: Central Alberta to southwestern Manitoba, south to Kansas and New Mexico, and west to north-central Arizona, Utah, east-central Idaho, and southwestern Montana.

Idaho Distribution: Foothills of the southern Beaverhead and Centennial Mountain Ranges in Clark County, the Henrys Lake area in Fremont County, and the Lemhi River drainage in Lemhi County.

References:

Barneby, R. C. 1964. Atlas of North American Astragalus. Memoirs of the New York Botanical Garden Vol. 13. New York Botanical Garden, Bronx, NY. 1188 pp.

Barneby, R. C. 1989. Intermountain Flora. Vascular plants of the Intermountain West, U.S.A. Vol. 3, Part B, Fabales. The New York Botanical Garden, Bronx, NY. 279 pp.

Isely, D. 1998. Native and Naturalized Leguminosae (Fabaceae) of the United States (exclusive of Alaska and Hawaii). Monte L. Bean Life Science Museum, Brigham Young University, Provo, UT. 1007 pp.