Physiognomy and Structure: Vegetation in this alliance is characterized by a moderate 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: This alliance is restricted to remnants of the Palouse Prairie. The vegetation is characterized by a moderately dense to dense graminoid layer dominated by medium-tall bunchgrasses Pseudoroegneria spicata, Festuca idahoensis, and/or Hesperostipa comata dominating the midgrass layer. Some stands have a short bunchgrass layer of Poa secunda. Species richness of perennial forbs can be low to high (up to 46 species), but their cover is generally less than 20%. Broad-leaved herbs typically contribute little to the composition of individual sites but may include Achillea millefolium var. occidentalis, Calochortus macrocarpus, Eriogonum heracleoides, Lithophragma glabrum (= Lithophragma bulbiferum), Lomatium triternatum, and annual Plantago patagonica. Scattered Ericameria nauseosa (= Chrysothamnus nauseosus) and Chrysothamnus viscidiflorus shrubs can be present to abundant especially on disturbed sites. Annual grasses and forbs are common and diverse, but many of them are non-native. Introduced annuals Bromus tectorum, Draba verna, Holosteum umbellatum, and Sisymbrium altissimum invade disturbed sites. Bromus tectorum can become permanently dominant in severely overgrazed stands. A diverse biological crust of moss and lichen can cover much of the space between vascular plants, although it can be displaced with ground disturbance.

Dynamics:  These grasslands are dominated by relatively deep-rooted grasses that use soil moisture below 0.5 m during the typically dry summers. The coarse-textured soils allow for rapid infiltration and storage of winter and summer precipitation (Kleiner 1968, Daubenmire 1970, Kleiner and Harper 1977, Thilenius et al. 1995). 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). However, burning generally kills or severely damages Hesperostipa comata plants. After fire, regeneration of this non-rhizomatous bunchgrass is through seed and may take many years to reach prefire densities (FEIS 1998).

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, Draba verna, Lactuca serriola, and Tragopogon dubius occur in many stands of the alliance and contribute significant cover on sites disturbed by livestock(Daubenmire 1970). The cool-season annual grass Bromus tectorum can be an effective competitor for winter soil moisture because it can germinate in the fall, overwinter, then begin regrowing in the early spring before it is warm enough for many perennial grasses, completing its lifecycle and depleting soil moisture before the dry summer weather begins. This annual species also produces abundant fine fuels that carry fire well and increase the frequency of fires (FEIS 1998).