What The Heck is a Milk-Vetch?

Coachella Valley milk-vetch | Photo: Keir Morse/Creative Commons License

The U.S. Fish and Wildlife Service announced this month that it had designated critical habitat for a plant called the Coachella Valley milk-vetch, which grows in sandy soil along the north edge of its namesake valley between Cabazon and Indio. About 9,600 acres of lands are covered in the final designation, mainly checkerboarded along washes and wind-blown sand corridors. The designation comes after 15 years of legal argument since the foot-tall plant was first added to the endangered species list in 1998.

If the critical habitat designation was based solely on science, there would probably be about 20,000 acres included, but even the slim level of protection afforded by that designation was fought hard by real estate developers in the Coachella Valley. And if it seems to you you've heard the word "milk-vetch" come up in other desert environmental issues, you're remembering right.

Though the Coachella Valley milk-vetch is protected as an Endangered species under the Endangered Species Act, it's not actually a species, but a variety -- Astragalus lentiginosus var. coachellae -- of a larger species, Astragalus lentiginosus. The entire species, often called "freckled milk-vetch,' is fairly common, ranging across the Intermountain West from British Columbia to Mexico. But the species is highly variable, with 40 formally recognized varieties. The Coachella Valley milk-vetch is the least abundant of those varieties, with only about 20 populations recorded in the last two decades -- all of them within three miles of Interstate 10.

The plant is short-lived: it's considered an annual, though occasionally an individual plant will survive for an extra year or two. In the legume family, it's readily identified by its deep purple blossoms and the subsequent freckled, inflated seed pods shown in the photo up top. As a desert annual, the milk-vetch can survive an unfavorable year by hiding as ungerminated seeds in the sand. Those seeds have a tough coat that must be scarified -- scratched up -- before water can penetrate to the seed within and spur germination. It can be tough to determine whether a seemingly barren patch of sandy soil holds a milk-vetch population.

There are a number of potential threats to the Coachella Valley milk-vetch. There's a huge amount of wind turbine development in the area, and off-road vehicle damage to the habitat is considerable. But the biggest problem is that the milk-vetch's habitat is ground zero for Riverside County's building boom. Even if a development doesn't directly pave over a milk-vetch population development in general has seriously altered the way sand moves through the Valley, and the plants require a fresh supply of sand to thrive.

When the Coachella Valley milk-vetch was listed as Endangered in 1998, a few of its cousins came with it. The closely related Fish Slough milk-vetch, Astragalus lentiginosus var. piscinensis, was listed as Threatened in the same move by FWS: a denizen of the similarly named wetlands north of Bishop, the Fish Slough milk-vetch is being edged out by cattle grazing and alterations to the wetlands that reduce its required alkali flat habitat.

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The Lane Mountain milk-vetch (Astragalus jaegerianus) and Pierson's milk-vetch (Astragalus magdalenae var. peirsonii) were also listed with the same stroke of FWS's pen back in 1998, as Endangered and Threatened respectively. Each of those milk-vetches starred in its own environmental protection drama. The Lane Mountain milk-vetch grows mainly on the Fort Irwin Army base, and was threatened for a time by the base's expansion of tank training grounds. And the Pierson's milk-vetch might well be the single organism most resented by hard-core off-roaders, as protecting it requires fencing off a large section of the Algodones Dunes to keep ORVs out, and the BLM is forever trying to whittle down the protected acreage to appease unhappy dune riders.

Why are milk-vetches so well-represented in environmental battles in the California desert? In part, it's because the milk-vetch genus Astragalus is a huge one, with about 3,000 species throughout the Northern Hemisphere. Some of its species are widespread, like the freckled milk-vetch, and some are quite rare. The Grand Canyon's sole federally listed Endangered species is a milk-vetch. There's a rare milk-vetch in Humboldt County that is not yet listed by FWS. In fact, a Google search on "Astragalus" and "Endangered" reveals that a lot of the Coachella Valley milk-vetch's cousins are in trouble.

Why is this? Blame evolution. Astragalus as a genus has some characteristics that allow it to survive in a wide range of places where other plants have trouble. As a legume, milk-vetches can take nitrogen from the air and use it as a nutrient, meaning that the plants can survive where others might starve. Astragalus' big, sturdy seeds offer seedlings a good-sized headstart, and the genus' habit of secreting toxic chemicals offers potential protection form grazing. (Another common name for the genus? "Locoweed.")

Over the centuries, milk-vetches have colonized most of the temperate parts of the northern hemisphere, evolving adaptations to a wide range of habitats. In much of the Intermountain West, including East California, those habitats are found in isolated patches surrounded by other kinds of habitat. If a plant population evolves fine-tuned ways of coping with a small patch of habitat, then it will likely have trouble when that habitat is threatened.

And so the Coachella Valley and Peirson's milk-vetches trade-off for their ability to grow in soils too sandy for other plants is that they can't escape that sand. When their sand is paved or trampled, they suffer. The Lane Mountain milk-vetch develops a way to twine its way up other plants, using them for structural support and shelter. When those other shrubs are demolished by tanks, the Lane Mountain milk-vetch loses its way of making a living. The Fish Slough milk-vetch evolves an ability to take advantage of the alkali flats that surround a seasonal desert wetland, and ties its fate irrevocably to those alkali flats. The sentinel milk-vetch finds a way to grow in the forbidding cliffs of the Kaibab limestone on the rim of the Grand Canyon, and before long it grows nowhere else. The gravel milk-vetch finds broad desert valleys filled with alluvium to its liking, and then finds out that that same habitat is highly desired by solar developers.

They range from well-protected to completely without protection, and grow in habitats from desiccated sand to isolated sodden marshes. One thing's for sure: whenevr someone decides to change a big swath of desert landscape of any kind, they're likely to find a milk-vetch got there before them.

Chris Clarke is an environmental writer of two decades standing. He writes from Joshua Tree regularly at his acclaimed blog Coyote Crossing and comments on desert issues on KCET weekly. Read his recent posts here and follow him on Twitter.

For ongoing environmental coverage in March 2017 and afterward, please visit our show Earth Focus, or browse Redefine for historic material.
KCET's award-winning environment news project Redefine ran from July 2012 through February 2017.

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