Physiognomy and Structure: Vegetation in this alliance is characterized by a sparse to dense cover of graminoids that is dominated by perennial bunch grasses less than 1 m tall. There is also sparse to moderate cover of perennial forbs. Occasional scattered shrubs and dwarf-shrubs may be present. Annual forbs and grasses are seasonally present.

Floristics: Vegetation of this alliance is characterized by a sparse to moderately dense herbaceous layer of graminoids, the most of common of which include Achnatherum hymenoides, Muhlenbergia pungens, and Pseudoroegneria spicata. Other common graminoid associates may include Festuca idahoensis, Hesperostipa comata (= Stipa comata), Koeleria macrantha, Leucopoa kingii, Pascopyrum smithii, Pleuraphis jamesii (= Hilaria jamesii), Poa fendleriana, Poa secunda, Redfieldia flexuosa, and Schizachyrium scoparium. Scattered shrubs may be found throughout stands, but only occur at low cover and may include Artemisia frigida, Artemisia nova, Artemisia tridentata, Cercocarpus montanus, Ericameria spp., Gutierrezia sarothrae, Krascheninnikovia lanata, and Tetradymia canescens. A sparse layer of forbs is typically present. Cushion plants may be important in some stands and may include species of Arenaria, Astragalus, Cryptantha, Heterotheca, Hymenoxys, Phlox, and Stenotus.

Dynamics:  Achnatherum hymenoides is one of the most drought-tolerant grasses in the western U.S. and occurs on a variety of xeric sites (USFS 1937). It is also a valuable forage grass in arid and semi-arid regions. Improperly managed livestock grazing could increase soil erosion, decrease cover of this palatable plant species and increase weedy species (USFS 1937). Fire has variable effects on Pseudoroegneria spicata. Plants usually survive burning, and growth is often stimulated, except when fire occurs in the driest month when the crowns will burn because of low moisture in the vegetation, and the meristems are damaged (Johnson and Simon 1987). Grazing impacts are concentrated on the gentler slopes accessible to livestock. Pseudoroegneria spicata shows an inconsistent reaction to grazing, increasing on some grazed sites while decreasing on others. It seems to recover more quickly from overgrazing than Festuca campestris (Mueggler and Stewart 1980). It tolerates dormant-period grazing well, but is sensitive to defoliation during the growing season. Light spring use or fall grazing can help retain plant vigor. It is particularly sensitive to defoliation in late spring (Comer et al. 1999). The exotic species Bromus tectorum occurs in many stands of the alliance and contributes significant cover on sites disturbed by livestock.