Alkali Milkvetch is a small, wispy-looking herbaceous annual herb. It is a California Native Plant Society List 1B species, or a plant that is rare, threatened or endangered in California. Photo courtesy of Tuleyome 

SACRAMENTO REGION, CA (MPG) - Alkali Milkvetch (Astragalus tener var. tener) is a member of the legume or pea family. The pea family is the third largest family of flowering plants with about 750 genera and well over 19,000 species identified worldwide.

In California alone, there are more than 3,000 recognized species. They can range from diminutive herbaceous annuals to woody vines and shrubs to statuesque trees. Commonly recognized members of this large family range from important agricultural crops such as alfalfa, beans, clover, peanuts, peas and soybeans to the California native Western Redbud and the pretty, yet toxic, wisteria vine.

Many members of this family have a symbiotic relationship with nitrogen-fixing soil bacteria making them vital to agricultural soil health and quality. The family is characterized in part by their distinctive flower parts and shapes and compound leaves but are probably most recognized by their fruits which resemble peapods or beans. Some species of milkvetch (Astragalus sp.) that occur in California thrive in habitats that would be inhospitable to most other plants.

As the name suggests, Alkali Milkvetch is associated with alkaline or saline soils and can tolerate a higher PH level than many other species. Alkali Milkvetch is endemic to California which makes it extra special because it only occurs here.

It is a California Native Plant Society (CNPS) List 1B species, a plant that is rare, threatened or endangered in California (and in other parts of its global range, however Alkali Milkvetch occurs only in California).

California Native Plant Society List 1B species have endured significant population plunges and might meet the criteria for special-status species listing under the California Endangered Species Act. Alkali Milkvetch is also listed as a federal Species of Concern under the Federal Endangered Species Act.

Alkali Milkvetch is a relatively small, wispy-looking herbaceous annual herb. It ranges from about an inch and a half to nearly 12 inches tall. The leaves are pinnately compound (structurally like a feather) and they have three to 12 densely arranged pink to purple pea type flowers with elongated pea-shaped fruits that are about an inch long at maturity.

Historically, Alkali Milkvetch occurred in vernal pool regions from the Central Coast, Sacramento, Salinas and San Joaquin Valleys and the Bay Area. Frequently, other associated special-status plants and wildlife species also occur where Alkali Milkvetch is present which often affords the surrounding vernal pool landscape conservation protection.

Alkali Milkvetch is not only endemic to California but also to its habitat of alkaline vernal pools from Sacramento to the Bay Area. Vernal pools are depressions in the landscape underlain by a hard, impermeable layer of soil.

During the rainy months these depressions fill with water as the surrounding landscape becomes saturated – picture a hole in a waterlogged sponge. During the cooler winter months, these ponded depressions support many miniscule but very significant common and special-status invertebrate species such as fairy shrimp, clam shrimp, seed shrimp, copepods, aquatic beetles, aquatic snails and more.

These invertebrates provide a major food source for amphibians, shore birds and waterfowl migrating through the Pacific Flyway. As the weather warms up, the ponded pools gradually dry down leaving behind vibrant concentric rings of stunningly colorful (and often endemic) plants and flowers.  During the hot and dry summer months, vernal pools dry out completely leaving the once inundated and chromatic depressions barren, cracked and sunbaked.

However, the dehydrated soil at the pool bottoms is deceptive because it is packed with cysts and seeds for the next rainy season’s crop of tiny but mighty fauna and flora. One of the special adaptations of vernal pool species is that cysts and seeds can remain dormant in the soil for years upon years until the necessary habitat conditions arise, a drought avoidance strategy beneficial to short-lived species.  Although other global Mediterranean climates also maintain vernal pools, California’s vernal pools support an immense diversity of plants and animals making them extraordinary.  It is believed that historically, California supported seven million acres of vernal pools, however today our state hosts less than ten percent of the original density as a result of land use changes and habitat fragmentation and degradation.

Although Alkali Milkvetch population numbers have been significantly reduced due to land use changes and loss of pollinators, there is a bright spot for the species. And it is nearly in our own backyards! Alkali Milkvetch was discovered in the vernal pools protected within the Woodland Regional Park Preserve (WRPP) boundaries.

Special care and consideration have been taken, and will continue, to ensure that the Woodland Regional Park Preserve design and encompassing walkways avoid the species and its habitat to preserve the populations on site. It is also believed that the species may benefit from managed grazing and other light land disturbances to help control competition from non-native species.

Recently, a relatively large Alkali Milkvetch population was discovered in vernal pools that are also known to support Vernal Pool Tadpole Shrimp (Lepidurus packardi), a federally endangered species near the city of Davis. Additional extant populations have been documented in Alameda, Napa, Merced and Solano Counties. Some of these populations are quite large and occur on protected land.

Conserving vernal pool landscapes preserves many endemic plant and wildlife species while also protecting an important part of California’s ecosystem.

Kristie Ehrhardt is Tuleyome’s Land Conservation and Stewardship Program Director. Tuleyome is a nonprofit conservation organization based in Woodland. For more information, go to www.tuleyome.org