Taxonomy
- Kingdom: Plantae
- Clade: Angiosperms → Eudicots → Rosids
- Order: Fabales
- Family: Fabaceae (legume family)
- Genus: Astragalus
- Species: Astragalus didymocarpus A.Gray
Common names
- Two‑carped milkvetch
- Twin‑fruit milkvetch (derived from the Greek roots didymo “twin” and carpus “fruit”)
Description
Astragalus didymocarpus is a perennial herbaceous plant that typically attains heights of 15–45 cm. The stems are erect, simple or occasionally branched, and may be glabrous or sparsely hairy. Leaves are pinnately compound, bearing 5–9 leaflets that are ovate to lanceolate, each 1–3 cm long, with entire margins and a slight pubescence on the underside.
The inflorescence is a raceme emerging from the leaf axils or terminally on the stem, bearing 10–30 flowers. Flowers are papilionaceous, characteristic of the Fabaceae, with a standard petal that is pink to purple, sometimes exhibiting a lighter hue on the keel. The calyx is tubular, usually 5–7 mm long, with sepals that are greenish‑brown.
Fruit is a leguminous pod, typically 1.5–3 cm in length, containing 1–2 seeds per pod—hence the epithet “didymocarpus” (paired fruit). Pods are straight to slightly curved, becoming papery and dehiscing at maturity to release the seeds.
Distribution and habitat
The species is native to western North America. Its range extends from central and southern Washington, through Oregon and Idaho, into northern and central California, Nevada, and western Utah. It occurs predominantly in dry, open habitats such as sagebrush steppe, chaparral, pinyon‑juniper woodlands, and montane meadows, typically on well‑drained rocky or sandy soils at elevations of 500–2,500 m.
Ecology
As a legume, A. didymocarpus forms symbiotic associations with nitrogen‑fixing rhizobia, contributing to soil fertility in its native ecosystems. The flowers attract a variety of pollinators, chiefly native bees (e.g., Andrenidae and Halictidae) and occasional butterflies. The seeds serve as a modest food source for small granivorous birds and mammals.
Conservation status
According to NatureServe, Astragalus didymocarpus holds a global status of G5 (Secure), indicating that it is widespread, abundant, and not currently at risk of extinction. No federal or state-level listings as threatened or endangered have been reported.
Subspecies and varieties
Two infraspecific taxa are recognized in some botanical references:
- Astragalus didymocarpus var. didymocarpus – the nominal variety, occurring throughout most of the species’ range.
- Astragalus didymocarpus var. latifolius – distinguished by broader leaflets and a more restricted distribution in southern California and adjacent Nevada.
Taxonomic treatment of these infraspecific ranks may vary among authorities.
Uses
There are no widely documented medicinal, agricultural, or horticultural uses for A. didymocarpus. The plant is occasionally noted in native‑plant restoration projects for its ability to improve soil nitrogen and provide habitat value, but it is not a major component of commercial cultivation.
References
- USDA, Natural Resources Conservation Service. “Plants Profile for Astragalus didymocarpus.” PLANTS Database.
- NatureServe Explorer 2.0. “Astragalus didymocarpus – Global Status.”
- Hitchcock, C.L. & Cronquist, A. (2018). Flora of the Pacific Northwest. University of Washington Press.
This entry summarizes currently available, peer‑reviewed, and government‑published information on the species Astragalus didymocarpus.