Ventura Marsh Milkvetch

(Astragalus pycnostachyus var. lanosissimus)

Ventura marsh milkvetch is a California endangered plant species, which means that killing or possessing any part of the plant is prohibited by the California Endangered Species Act (CESA). This species is also listed as endangered under the federal Endangered Species Act (ESA). Ventura marsh milkvetch was thought to be extinct until it was rediscovered in 1997 at an abandoned oil-field waste site near Oxnard. This is the only extant “wild” population according to the California Natural Diversity Database (CNDDB). “Wild” is in quotations because this site had been completely modified by human activities and is unlike any nearby coastal habitat. The population is found on artificially compact substrate composed of clay, sand, and small gravels with a water table three to five feet below the ground surface.

Ventura marsh milkvetch is a short-lived perennial herb in the legume family (Fabaceae) and is endemic to California. It has numerous yellow-white to cream pea-like flowers arranged in dense clusters that bloom from June to October. The leaves are pinnately compound and densely covered with soft silver-white hairs. Historically, Ventura marsh milkvetch was found along the coast of Orange, Los Angeles, and Ventura counties on well-drained soils in coastal shrublands, marshes, swamps, and coastal dune swales with a relatively high water table near bodies of fresh or brackish water. It is found in association with other coastal shrubland species such as Acmispon glaber, Ambrosia chamissonis, Camissoniopsis cheiranthifolia, Baccharis pilularis, Malosma laurina, and Salix lasiolepis. The flower structure of Ventura marsh milkvetch requires insects to manipulate the flower parts for successful pollination. Researchers have observed bumble bees (Bombus spp.), carpenter bees (Xylocopa spp.), marine blue butterflies (Leptotes marina), common hairstreak butterflies (Strymon melinus), skippers (family Hesperidae), and honey bees (Apis mellifera) visiting the flowers. The number of observed seeds per fruit are relatively low compared with other milkvetch species, indicating that seed production may be limited by pollination.

Many factors have been responsible for the decline of Ventura marsh milkvetch over time. Habitat loss and degradation due to nearby urban development coupled with invasive species encroachment led to the apparent extinction of the species prior to 1997. There have been several attempts to establish populations of Ventura marsh milkvetch within and outside its historical range. The results of these outplantings have varied and many have failed, however, currently there are two sites that are starting to establish with increasing numbers of volunteer recruits. The challenges facing recovery and recruitment efforts for this species include small population numbers resulting in low genetic diversity, fruit and seed herbivory, declining pollinators, altered hydrology due to urban development, and the ongoing threat of climate change. The success of outplantings relies on constant management and will be critical for the continued existence of the species. The survival of Ventura marsh milkvetch will also require establishment of additional populations and ongoing scientific and conservation work.

CDFW has participated in the following Ventura marsh milkvetch studies with support from the Cooperative Endangered Species Conservation FundCooperative Endangered Species Conservation Fund. (opens in new tab).

CDFW may issue permits for research and recovery of Ventura marsh milkvetch pursuant to CESA, and you can visit our website to learn more about the California Laws Protecting Ventura marsh milkvetch and other California native plants. Populations of Ventura marsh milkvetch occur in CDFW’s South Coast Region. More information on Ventura marsh milkvetch is also available from the United States Fish and Wildlife Service Species Profile for Ventura marsh milkvetch.

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Dense cluster of yellow pea-like flowers and pinnately compound leaves with soft white hairs
Astragalus pycnostachyus var. lanosissimus, CDFW Photo by Jeb Bjerke
Ventura marsh milkvetch habitat of a variety of coastal shrubs
Astragalus pycnostachyus var. lanosissimus habitat, CDFW Photo by Jeb Bjerke