Grazing Oklahoma: Tharp’s Spiderwort

(Photo courtesy of the Noble Research Institute)

By Mike Proctor, Noble Research Institute research associate /

Characteristics: Some say Spiderworts get their name from their sticky sap, which resembles a spider web after drying. Others say it is because their leaf arrangement resembles a squatting spider. I’m inclined to go with the first opinion, but if you’d really like to avoid conflict, you can just call it cow slobber and avoid the issue entirely.

The genus is named after John Tradescant, botanist and gardener for the king of England in the early 1600s. This particular species was named after Benjamin Tharp, a botanist at the University of Texas. Eight species of spiderworts occur in Oklahoma, all of them native. The common houseplant, Wandering Jew, is a tropical species of Tradescantia.

Few plants in the prairie show off quite like this one. It’s hard to miss bright yellow stamens contrasting against a background of purple petals in a sea of green grass. Tharp’s spiderwort is a short herb, less than one foot tall, with long leaves about one-half inch wide. Even when abundant, it is rarely noticed unless flowers or fruit are present because the leaves, which resemble grass blades, blend in with the other vegetation.

The flowers range in size from one-half-inch to nearly three inches, and in color from light pink to a dark purple. The flower size decreases later in the season as soil moisture decreases and daytime temperatures increase. Individual flowers open in early morning and usually only last until the afternoon.

Area of importance: In Oklahoma, Tharp’s spiderwort occurs mostly in the eastern two-thirds of the state. Its habitat is grasslands, often on rocky soil, and usually with quite a bit of clay. It is rarely tall enough to be seen above the grass from the road; you have to wade out into the chiggers to really see it. Since it likes clay, you’re unlikely to see it in the company of trees, unless the cedars and hackberries are invading. I see it most often growing with Texas Needlegrass and Sideoats Grama.

Attributes: Native pollinators use the flowers, and a variety of vertebrates, including livestock, utilize the leaves as forage, although I doubt it is ever abundant enough to be useful for livestock.
When cultivated, flowering continues later into the year in the shade and when watered regularly, as do many native species. Several related species and cultivars are available commercially. Most of the species can be started from seed.

Native Americans used a related species, T. virginiana, to treat insect bites, cancer and some stomach-related problems, as well as using the greens for food. A recurring theme in many of the sources I used to research this plant was the lack of insect pests. This makes me wonder if it might have some insect repellant properties as well.

Studies done in Japan on a couple of different speces of Tradescantia have shown that small amounts of radiation can cause mutations in the hairs around the stamens as they are growing, causing them to change color. Mutations occurred at radiation levels that had previously been considered safe. A system has even been developed to use this response to test for radiation and other mutagens. It’s hard not to like a plant that brings its own Gieger counter.

So the next time someone asks me why I’m standing out in the pasture staring at the ground, rather than telling them that I’m sampling species composition, I can say checking for radiation.

I have a hunch they’ll find someplace else they need to be pretty quick.