I was hiking on a nearby ranch last week when we came across some spectacular wildflowers. As I knelt to grab some photos, my plant expert companion remarked, “You know that’s locoweed. We should pull it out!”

What? Destroy these beauties? Why? I was about to receive an education.

Locoweed (or crazyweed) is the common name for two genera of western plants, Oxytropis (left) and Astragalus (also called milkvetch), both in the pea family, and both including some species that contain the toxin swainsonine. Swainsonine interferes with protein metabolism and causes nerve damage.

Animals that eat plants containing swainsonine grow lethargic, become unable to eat, and, if they’re consumed enough of the toxic chemical, they die from either starvation or mishap. Other symptoms include sterility, birth defects and spontaneous abortion, depression, weakness, and heart failure. There is no treatment or cure. Even if the animals survive an initial poisoning, the damage is permanent. Clearly, anyone grazing animals in the western U.S. needs to know what locoweeds look like.

Like other pea family plants, locoweed has pinnate leaves. This means they look like a feather, with a long, central stalk with opposing pairs of leaves down its length. The many stems form a clump that can be four to twelve inches tall. Showy flowers look like peas and come in white, yellow, blue-purple, or bright purple-pink. In the genus Oxytropic, the flowers have distinctive pointy “keels.”. As you would expect, seeds form in long pods.

Locoweeds are resilient plants, surviving drought and heat, and are usually found in the foothills and dry short-grass prairies.

The problem is that these locoweeds are particularly tasty to horses, sheep and cattle, as well as occasional deer and elk, and often appear early in the season when healthier forage isn’t yet available. Even the dead and dried winter foliage is palatable. In fact, it’s addictive.

It’s particularly frustrating to wildflower lovers that such gorgeous plants endanger livestock and need to be destroyed. Ranchers spray with herbicides, although with thousands of acres to patrol, the time and expense add up quickly. More helpful are several types of insects that can chew through entire patches, providing some measure of control. They even hang around to consume new seedlings, a real benefit since seeds stay viable in the soil for up to fifty years.

One promising avenue of research is based on the interesting possibility that swainsonine may not be produced by the plants themselves. Rather,  the toxin might come from fungi living inside the plants’ tissues. If a way can be found to kill the fungi without harming the plants, we can have our steaks and flowers too.

In control is attempted, correct identification is critical. Many Astragalus species are perfectly safe for range animals. Additionally, some locoweeds are rare, and at least one species, Astragalus holmgreniorum, and numerous subspecies in both genera, are federally listed as endangered.

My hiking companions and I did pull out that locoweed plant, as well as all the others we came across that day. At least I got my pictures first.