Alkali Milk Vetch (Astragalus tener var.tener)

Along with the sunflower (Asteraceae) and the grass (Poaceae) families, the legume family (Fabaceae-also called Leguminosae) ranks among the most species-rich families of flowering plants, consisting of some 650 genera and 18,000 species worldwide. The family is divided into three subfamilies, the mimosas, the sennas, and the beans. Members of the family range from vines to herbs to shrubs to trees, occupying a tremendous variety of habitats in tropical, subtropical, and temperate regions. The legume family is of extreme importance to humans, providing an important source of protein, timber, dyes, animal fodder, as well as plants of ornamental value. Economic crops include peanuts, soybeans, clovers, garden peas, lentils, lupines, wisteria, wattle, mesquite, tamarind, and even the dreaded French broom. A unique feature of most legumes is the presence of root nodules containing bacteria (Rhizobium spp.), which are capable of converting atmospheric nitrogen into other nitrogen compounds readily usable by plants. Crop rotation, incorporating a legume every three years, can substantially replace the nitrogen used up by other crops.

In California, the legumes are also only second to the sunflower family in terms of the number of species that have naturalized here. The Jepson Manual lists 50 genera, 29 of which include at least some native taxa. Some of the more recognizable genera include western redbud (Cercis occidentalis), broom (Genista), wild pea (Lathyrus), lotus or deer weed (Lotus), lupine (Lupinus), the clovers (Trifolium), and, of course, milk vetch or loco weed (Astragalus). Of the 1,742 taxa listed in the CNPS’s Inventory of Rare and Endangered Vascular Plants of California, 76 (4.4%) belong to the Fabaceae. Fifteen of these are state- and/or federally-listed as Endangered, Threatened, or Rare.

Astragalus is perhaps the most species-rich genus of all flowering plants, comprising an estimated 2,000 taxa worldwide. California alone boasts 142 indigenous species, subspecies, and varieties. In California, the genus is unique for the lack of non-native taxa; none are listed in The Jepson Manual. The milk vetches belong to the subfamily Papilionoideae. With the exception of western redbud, all of the genera listed above are in this subfamily.

Alkali milk vetch is an annual herb inhabiting playas, clay soils supporting valley and foothill grasslands, and alkaline, vernal pools. It occurs in open, alkaline and vernally moist meadows from sea level to 200 feet in elevation. It is believed extant in Alameda, Merced, Napa, Solano, and Yolo counties. It is believed extirpated from Contra Costa, Monterey, San Benito, Sonoma, and Stanislaus counties. Threats to the species include habitat destruction, especially agricultural conversions. Alkali milk vetch was last collected in the Bay Area in 1959. It is protected at the Jepson Prairie Preserve. Alkali milk vetch is known from San Francisco from historical records. It was purportedly identified in 1868 by Kellogg and Harford, occurring in low, sub-saline fields in the Mission Dolores area.

Alkali milk vetch is a delicate, sparsely hairy to smooth herb, growing one to twelve inches high. It has seven to seventeen leaflets on blades one to three-and-a-half inches long. It produces two to twelve pink-purple flowers per inflorescence. Fruits are elongated legumes under an inch long. The variety flowers from March through June.

Alkali milk vetch is not listed by the state of California or the federal government, so it is afforded no protection under the state or federal Endangered Species Acts. It is on the CNPS List 1B 3-2-3. This status indicates that the variety is rare, threatened, or endangered in California, is distributed in a limited number of occurrences, is endangered in a portion of its range, and is endemic to California. List 1B species meet the criteria for listing pursuant to the state Fish and Game Code, and impacts must be considered during preparation of environmental documents relating to the California Environmental Quality Act (CEQA). Unfortunately, unless a species is formally listed as endangered, threatened or rare by the state or federal governments, it has no official protection. CEQA provides for the protection of these “special-status species” only so far as the lead agency is willing to incorporate comments from the public, the CNPS, or the Department of Fish and Game.