• Double O Arch


    National Park Utah

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Crescent Milkvetch

Astragalus amphioxys

Astragalus amphioxys var. amphioxys

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

Perennial herbs from a taproot; 0.8” to 1.2' (2 to 35 cm) tall

Leaves: alternate; compound; 0.08” to 0.52” (2 to 13 mm) long; leaflets 0.12” to 0.8” (3 to 20 mm) long; 0.04” to 0.36” (1 to 9 mm) wide

Flowers: rarely flowers the first year; 5 lobed petals (a banner, 2 wings and 2 keels); 5 toothed sepals; bisexual; pink, purple, or rarely white; 10 to numerous stamens, 1 pistil; flowers 0.66” to 1.24” (16.5 to 31 mm) long

Pollinators: other Astragalus species are pollinated by insects (specifically 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: around Visitor Center buildings, park road mile 0 to 2.5, Courthouse towers, Windows, park road mile 9.8, outside Arches National Park on Portal trail

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, “amphioxys”, is possibly from the Greek “amphi” meaning “both kinds of or double” and "oyxs" meaning “sharp” in reference to the pointed ends of the seedpods.

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?

Collared Lizard

Lizards, including the colorful collared lizard, are one of the most frequently seen animals at Arches. When not chasing flies or basking in the sun, they are often seen doing what appears to be push-ups. This odd dance might enhance their stereoscopic vision, helping them see what's looking back at them.