Photo © Robert K. Moseley
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Astragalus drummondii Douglas ex. Hook.

Drummond's milkvetch

Fabaceae (Pea; Legume family)

General Description: A stout, villous-hairy, perennial forb with several erect stems 25-55 cm tall. The compound leaves have 13-33 oblong-elliptic to obovate, obtuse or notched bicolored leaflets that are pale green beneath and bright green above; the larger ones 12-30 mm long. Racemes have 15-30, nodding, white to yellow-white flowers on stout, erect stems 4-14 cm long. Banner petals are 15-25 mm long and the keel petal lilac-tipped. The calyx is 7-13 mm long and commonly has black hairs. The stipitate, hanging fruit pods are 17-32 mm long by 3-6 mm wide and more or less linear in profile with three blunt angles. Pods are green and totally hairless, have a prominent brown suture, and become almost leathery in age.

Photo © Robert K. Moseley
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Field Identification Tips: Drummond's milkvetch is recognized by its coarse habit, foliage with spreading hairs, large, whitish, nodding flowers, and pendulous, stipate, glabrous pods.

Illustration.

Phenology: Flowers in late spring, usually peaking in June and done by early to mid-July.

Similar Species: None of the several other Astragalus species that could co-occur in Idaho, such as Astragalus miser (weedy milkvetch), A. convallarius (lesser weedy milkvetch), A. cibarius (browse milkvetch), and A. lentigenosus (freckled milkvetch) should be confused with Drummond's milkvetch. Larger flowers, and several features of the fruit pod will distinguish Drummond's milkvetch from A. bisulcatus var. bisulcatus (two-grooved milkvetch).

Habitat: In Idaho, Drummond's milkvetch occurs in sagebrush-bunchgrass habitats on open, gentle to moderately steep, predominately south- to west-facing slopes with gravelly to rocky soils. Associated species include Artemisia tridentata ssp. vaseyana, Chrysothamnus spp., Tetradymia canescens, Festuca idahoensis, and Pseudoroegneria spicata.

Global Distribution: Widespread over the high plains and Rocky Mountains from southern Canada, south to New Mexico, and entering the Intermountain region in portions of Utah and eastern Idaho. It is most common along the east slope of the Rockies and adjacent plains.

Idaho Distribution: Sagebrush plains and lower slopes along the southern Beaverhead and western Centennial ranges in northern and central Clark County. Also known from the eastern base of the Lemhi Range in the Birch Creek Valley, in the southwestern corner of Clark County.

References:

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.