Purple thee-awn is a warm season bunchgrass, meaning it's slow to start and really gets going after other species like prairie junegrass have gone to seed. It is short and compact, with thin delicate foliage and interesting little seeds that disperse via three long awns that catch the wind. 
 
This species grows on very dry and often rocky slopes, and is one of the toughest little grasses out there. I collect the seeds from the nursery property up in the Moiese hills near Charlo, where it holds its own agains large herds of deer in the winter and stray cattle in the summer. While some of our dryland bunchgrasses handle extra water, this is NOT one of those species. Dry. Very dry. 
 
This grass is a perfect compliment to prairie and sage grassland plantings, and adds diversity to prairie junegrass/Idaho fescue/bluebunch wheatgrass assemblages. From my observations, it seems to enjoy the company of: white prairie aster, hairy golden aster, shaggy fleabane, twin arnica, bluebunch wheatgrass, Idaho fescue, and prairie junegrass.