3 Awn Grassor

3 Awn Grassor

3 Awn Grass

This is a perennial bunchgrass, growing erect to under a meter-3 feet in height, and the flower glumes often assumes a light brown to reddish-purple color. There are several varieties with overlapping geographical ranges. This is not considered to be a good graze for livestock because the awns are sharp and the protein content of the grass is low.


This distinctive arrangement of three long, stiff bristles arising atop a slender achene tells us that we have a three-awn grass, a member of the genus Aristida. About 300 Aristida species are recognized worldwide, mostly growing in arid, warm regions like here; about 19 Aristida species are listed for Texas. The species in our picture seems to be the three-awn grass most typical for openings in forests of Texas Live Oak and Ashe Juniper, ARISTIDA PURPUREA, often known as Purple Three-awn Grass. It's found on dry, rocky soils on the Great Plains from Utah, Colorado and Kansas south through our area into northern Mexico.Back when vast herds of buffalo roamed the American prairies this was one of the medium-size grasses they might have munched on if the herd wandered into dry, rocky spots. However, for grass eating herbivores Purple Three-awn Grass isn't a particularly palatable species, since its nutrient value isn't as good as some other species, plus, when the grass is fruiting, those long bristles stick in a grazer's throat and can cause sores in the stomach.

Until I saw the three awns shown in the last picture, I had no idea who the grass was causing the purple patches, but seeing those awns suddenly it occurred to me that we've already examined this species. Last September we looked at Purple Three-awn Grass, Aristida purpurea, and that's what we have again. Except that last September the grass was dry and straw-colored, and the awns atop the grass's matured grains stuck out at right angles to the grains, giving the fruiting heads a spiky look, as shown in our photo at the top of this page. The Aristida genus is a fairly large group of small to medium sized, clump forming grasses that are mostly associated with dry, sandy soils. They are commonly called three-awn grasses due to the three-parted awn at the tip of the lemma. Structurally there is a central and two lateral awns and the relative differences in length and degree of twisting of these awns is a primary diagnostic to their identification; many are readily distinguished on this characteristic alone, but the twisting may not be distinctive until maturity. There are six species found in Minnesota, and while three of the six are state listed as rare, from a field encounter perspective, the other three are relatively uncommon but for a few specific sites. (Source: www.minnesotawildflowers.info)


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