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Rimrock Milkvetch

Astragalus desperatus

Astragalus desperatus var. desperatus

Family: Fabaceae (A Utah Flora – Leguminosae) – Pea Family

Perennial herbs; 0.4” to 1' (1 to 30 cm) tall

Leaves: alternate; compound; 7 to 17 leaflets 0.08” to 0.52” (2 to 13 mm) long, 0.04” to 0.2” (1 to 5 mm) wide; leaves 0.4” to 4.8” (1 to 12 cm) long

Flowers: 5 pink or purple petals (a banner, 2 wings and 2 keels); keel shorter than the wings; 5 toothed sepals; bisexual; 5-10 stamens, 1 pistil; flowers 0.24” to 0.36” (6 to 9 mm) wide

Pollinators: other Astragalus species are pollinated by bees, moths and butterflies

Fruits: legume

Blooms in Arches National Park: January, February, March, April, May, June

Habitat in Arches National Park: desert shrub and pinyon-juniper communities

Location seen: park road mile 0 to 2.5, Delicate Arch trail, outside Arches National Park in Negro Bill Canyon

Other: The genus name, “Astragalus”, is the Greek name for “legume”, and may be derived from “astragalos” which means “ankle bone” referring to the shape of the leaves or the pods. The species name, “desperatus”, is one of the more humorous scientific plant names. It was named in 1891 by Marcus Jones who was “desperate” to find a name not already taken in the Astragalus genus (information about the species name from Al Schneider, www.swcoloradowildflowers.com).

This plant is endemic to Emery, Garfield, Grand (type specimen was collected near Cisco), Kane, San Juan and Wayne Counties in Utah and adjacent areas in Colorado and northern Arizona.

This family is ranked second to grasses in importance to people because species can fix nitrogen. However, some species, e.g., locoweeds and milkvetches, are poisonous due to selenium abstracted from the soil.

Did You Know?

Close up of biological soil crust

The dirt is alive! A living crust called "Biological Soil Crust" covers much of Arches and the surrounding area. Composed of algae, lichens and bacteria, this crust provides a secure foundation for desert plants. Please stay on roads and trails to avoid trampling this important resource. More...