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Astragalus diversifolius Barneby

Meadow milkvetch

Fabaceae (Pea; Legume family)

General Description: A diffuse or prostrate perennial forb with weak, slender, sparsely leafy, simple or branched stems radiating from the root crown. Leaves are 2-5.5 cm long, with 1-5 linear, grasslike, or ovate leaflets 2-5 mm broad. The terminal leaflet is always the longest and continuous with the leaf stalk. The inflorescence is a loose raceme of 2-8 white, cream, or yellowish-white flowers. The flowers are often faintly purplish-tinged/tipped, with the banner petal being 7-13 mm long. The calyx is 3.5-6.5 mm long and has short, appressed, black or white hairs. Fruit pods are oblong, straight or slightly curved, 10-17 mm long by 3-4 mm broad, with the thin green pod becoming papery and straw or gray-brown colored.

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Illustration.

Field Identification Tips: The slender, often prostrate, sparsely leafy habit of meadow milkvetch, combined with a terminal leaflet larger than the lateral leaflets, makes this species relatively easy to identify. However, these same features can make it difficult to see in the field, especially if done flowering. The narrow leaflets mimic blades of grass and the whole plant becomes seemingly hidden in the vegetation.

Phenology: Plants begin to flower in June and peak during July. More fruits than flowers are observed by August.

Similar Species: Meadow milkvetch is most likely to be confused with other diffuse-looking, sparsely leafy Astragalus species occurring within its range. Astragalus convallarius (lesser rushy milkvetch) has narrow fruits over 20 mm long, very narrow leaflets, and occurs in drier habitats. Astragalus ceramicus (painted milkvetch) has inflated, reddish- to purplish-mottled pods and occurs in dry, sandy habitats. Astragalus leptaleus (Park milkvetch) occurs in several of the same east-central Idaho wetland systems as meadow milkvetch. It is readily distinguished by having leaves with 15-25 leaflets, smaller flowers, and an inflorescence that does not extend much above the middle of the plant.

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Habitat: Moist soils in alkaline meadows with flat or hummocky topography supporting graminoid or medium height shrub vegetation. Associated species may include Juncus balticus, Poa secunda, Leymus cinereus, Spartina gracilis, Senecio debilis, Phlox kelsyi, Glaux maritima, Sarcobatus vermiculatus, and Potentilla fruticosa.

Global Distribution: Widely separated populations are known from east-central Idaho, the southwestern edge of the Salt Lake Desert in western Juab and Tooele counties, Utah, and the Spring Valley area in southern White Pine County, Nevada. There is also a historical record for this species from the Green River Basin in western Wyoming.

Idaho Distribution: Most Idaho populations are located in Custer and Lemhi counties, in the intermountain valleys of the Big Lost, Little Lost, Pahsimeroi, and Lemhi rivers, and Birch Creek. The meadow milkvetch population reported from the upper Snake River Plain, near Springfield, in Bingham County, has probably been extirpated.

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.

Wyoming Rare Plant Technical Committee. 1994. Wyoming rare plant field guide. USDI Bureau of Land Management; National Park Service; Fish and Wildlife Service; USDA Forest Service, Intermountain Region and Rocky Mountain Region; Wyoming Game and Fish Department; and The Nature Conservancy, Wyoming Natural Diversity Database.