These plants of the Fabaceae family grow anywhere from six to eighteen inches high and are capable of living in or near sagebrush scrub, shadscale scrub, alkali sinks, subalpine forest, foothill woodlands, yellow pine forests, valley grasslands, creosote bush scrub, Joshua tree woodlands, on dunes or in any generally dry, open places.
In addition to thriving in the Mojave Desert, these plants are present in the High Sierra Nevada, Sierra Nevada, Tehachapi Mountain Area, San Joaquin Valley, San Francisco Bay Area, Inner South Coast Ranges, and the Great Basin Floristic Province. They have been found at elevations from one hundred feet below sea level to 11,700 feet.
Clusters of anywhere from three to 50 flowers sprout on the plant’s arched and reddish stem that is composed of a main branch or a complicated arrangement of branches that ascend or spread, with purplish, pink, cream, whitish or mixed purplish ad whitish petals. Leaflets are a half inch to six inches in size, are ovate and most often silver-green in color.
The plant features a mottled, papery pod/fruit that is bladder-like. The common name freckled milkvetch is a reference to these somewhat hairy seed pods, which have a mottled, red/cream coloration, a groove down one side, and a sharply pointed tip. The seeds contained in the dried pod will make a rattling noise, which is the basis for one of its common names, rattleweed.
Stems and leaves may be hairy or hairless, though the species is generally less hairy than most other members of its genus. The leaf edges are also often reddish.
These plants are also referred to as loco weed, but should not be confused with several other plants also referred to as loco weed, or one in particular, jimson plant or jimson weed, Datura stramonium.
Astragalus lentiginosus is referred to as loco weed because cattle and horses display unbalanced behavior after eating this plant, a phenomenon first noted by the Spanish inhabitants of the southwest who witnessed their animals acting crazily or “loco” in Spanish.
Most varieties of Astragalus lentiginosus flower from March through June with a few varieties also flowering during September and October.