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
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
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.