The name “locoweed” conjures up the classical desert image: a sun-baked landscape littered with bleached bones of creatures and a mad cow bucking and spinning in the far distance.

Growing in the foreground of this desolate landscape are some locoweeds or members of the Astragalus genus. The cow is not mad mad, but “loco” mad.

Because of this image, locoweeds get a bum-rap. With over 2,000 different species in the Northern Hemisphere, some members of this group are actually good forage plants. Few, but not many. Their toxicity is not directed solely at grazing cows, but as a defensive mechanism against all grazers. Cows, sheep and horses just have a harder time getting the idea of not eating these plants through their skulls.

The name Astragalus comes from the Greek word meaning “anklebone.” One of the 7 bones in a goat or sheep’s ankle (known as the “knucklebone”) was used by the ancient Greeks as 4-sided dice. Plural, they were known as astragaloi. “Roll them bones,” is a Vegas crapshooter’s chant. Perhaps the connection between locoweeds and dice is when the seeds rattled around inside the inflated pods the sound was reminiscent of dice in a cup. That or you have to be loco to play craps in Vegas.

In the desert in May, locoweeds or milkvetches abound. The common name “milkvetch” comes from the belief that goats feed a diet of Astragalus cicer, an Old World species, increased their milk production. However, many of the western locoweeds are toxic to livestock as the plants uptake selenium from the soil or manufacture locoine – a designer alkaloid - to make themselves less palatable. For those creatures that ignore this warning, there may be dire consequences of general weakness, loss of neural control, staggering, convulsions, blindness, paralysis, and death.

When livestock eat locoweed over a period of several weeks to a month, these symptoms of locoism or “loco disease” start to manifest. If sufficient forage is available, the animals often avoid the locoweeds. However, some animals become hooked like junkies and actually seek out the plants. Longevity for them is not a sure bet.

Toxicity aside, there is a wide variety of locoweeds that bloom in the desert and provide pollen and nectar rewards for pollinators. Two of the locoweeds with lighter-colored flowers are the stinking milkvetch (A. praelongus) and the yellow milkvetch (A. flavus). The stinking milkvetch has thick clusters of flowering stems that may rise 2-3 feet. The tightly clustered flowers are cream-colored, almost tubular in shape, and are often tipped with purple. The plant’s unpleasant odor indicates its common name. Another common name for this plant is “rattlepod,” for the plant’s seeds rattle around the dried seedpods during a light wind.

Growing in clay-rich soils, the yellow milkvetch is named after the flower’s color. The leaflets are narrow or egg-shaped and may bear short, stiff hairs. The bell-shaped flowers grow in tight clusters and, like many of the locoweeds and milkvetches, attract a wide variety of bees as pollinators.

There are several common locoweeds that bear pinkish or purple-colored flowers here, as well. One prominent species that seems to thrive along the edges of roadways (due to water runoff from the pavement) is the Preuss’ milkvetch (A. preusii). The plant’s reddish stems arise from a woody base and bear pinkish, white, purplish, or bi-colored flowers that flare dramatically at the tips. Named after Charles Preuss (1803-1854), a topographer who joined John C. Frémont’s western expedition in 1843-1844, this milkvetch may bloom in excess during wet years.

Another prominent locoweed that may grow in abundance is the woolly locoweed (A. mollissimus). Mollissimus means “most soft” and describes the texture of the woolly leaflets. The long tubular flowers bear very hairy, egg-shaped pods.
Though the woolly locoweed and Preuss’milkvetch are prominent members of this club, my favorite is the low-growing painted milkvetch (A. ceramicus). The small flowers are dull pink and the leaflets are long and threadlike. Seemingly lacking of showy characteristics, these plants produce inflated pods decorated with ceramiclike markings.

Even though the locoweeds and milkvetches can grow in soils that remind one of a bleak and lonely landscape, this should not detract from their interest. Locoweeds exhibit a great deal of diversity, grow from bleak deserts to alpine habitats, and, like many members of the Pea Family, are able to transform atmospheric nitrogen into a valuable soil nutrient. So remember the sage advice from The Sierra Club Naturalist’s Guide to the Deserts of the Southwest when you are out looking at locoweeds: “Don’t eat the leaves.” It’s in your best interest, and that is a sure bet.