Aristida purpurea Nutt.
Scientific Name Synonyms:
Aristida longiseta Steud.
Life Span: Perennial
Growth Characteristics: A tufted bunchgrass, without rhizomes, growing 8 to 16 inches tall, with fine stems. Starts growth in late spring and produces abundant seeds. Red Threeawn reproduces from both seeds and tillers.
Seedhead: Narrow to moderately spreading panicle, often over 6 inches long; spikelets few, on pedicels, contains 1 floret, purplish-red at maturity; lemma awn three-branched, 2 to 4 inches long and spreading at maturity; seed enclosed by the awned lemma.
Leaves: Glabrous except at collar; leaf blades narrow, rolled, rather stiff, up to 6 inches long, about as long as culm; leaves rolled in the bud; hairy at collar; ligule a fringe of short hairs; auricles absent.
Red threeawn is a strongly competitive native grass. If it dominates a site, it is often and indicator of disturbed sites (i.e. roadsides), or long-term, heavy, season-long use. It is common to upland and semi-desert sites and has an ecological advantage in the shallower soils on these sites. It is more common in the southern and lower elevations of the state of Utah, being found at elevations between 2,500 feet and 9,000 feet, and in the 8 to 14 inches annual precipitation zone.
Soils: It is most adapted to sand or sandy loam soils, but does well on stony, gravelly soils.
Associated Species: Big sagebrush, cheatgrass, needle-and-thread, western wheatgrass, blue grama, and annual forbs.
Uses and Management:
The phenology of this plant explains its grazing response. It is poor forage for both livestock and wildlife. It is worthless for forage in the winter, although it may be used during drought years. By starting its growth late in the growing season, it allows it to escape from grazing. It has excellent drought resistance, giving it an advantage over the other plants that are grazed during both the early and late season. The awns may decrease fleece value, and may also cause irritation and abscesses in the mouths and nostrils and damage the eyes of grazing animals.
The excessive presence of red threeawn is an indicator of the need for range improvement.