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NATURAL HISTORY

HOLMGREN’S MILK VETCH } Astragalus holmgreniorum
FAMILY: Fabaceae


|DESCRIPTION: The Holmgren’s milk vetch is a stemless, herbaceous perennial that produces leaves and small purple flowers in spring — both of which die back to the plant’s roots after flowering season. The distinctive, pea-like flowers of Holmgren’s milk vetch are about two centimeters long, while fruit pods are three to five centimeters in length.

HABITAT: Holmgren’s milk vetch is a narrowly distributed, Mojave Desert endemic restricted to shallow, sparsely vegetated, limestone-derived soils at elevations between 2,480 and 2,999 feet.

RANGE: Three small metapopulations of Holmgren’s milk vetch exist in Washington County, Utah, and adjacent Mojave County, Arizona.

LIFE CYCLE: Holmgren’s is an extremely short-lived perennial herb with low survivorship from germination to one-year-old juvenile or reproductive adult. Few plants live past two growing seasons, and fewer than 2 percent of seedlings typically live into their fourth growing season. Plants entering their second year of growth or older appear several weeks before seedlings in late February or early March; plants flower between March and April and set fruit by the end of April, with seed pods persisting until the end of May. The plants then die back to their roots between late May and mid-June.

THREATS: Urban development, off-road vehicles, livestock grazing, displacement by exotic plants, and mining pose significant threats to the Holmgren’s milk vetch.

POPULATION TREND: The milk vetch is declining.

Holmgren's milk vetch photo © Renee VanBuren