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Description and adaptation
Annual hairgrass is a fine textured, native, cool season grass with smooth, slender stems (culms) that are 10 to 60 cm tall. The form is upright to spreading, short, and somewhat tufted. The narrow leaf blades are hairless, rough on the edges, slightly in-rolled, 0.5 to 1.5 (2) mm wide, and 1 to 10 cm long. Flower heads (panicles) are open, 7 to 25 cm long, with ascending lower branches. Annual hairgrass occurs from near sea level at the coast to 8000 feet in the Rocky Mountains. It is primarily found from Alaska south to Baja California and east to Montana and New Mexico; also the Northeast US and Chile.
Key to identification: Annual hairgrass can be distinguished from slender hairgrass (Deschampsia elongata) and tufted hairgrass (Deschampsia caespitosa) by its weaker root development, fewer leaves, and smaller stature. Without close inspection it may be confused with other annual grasses, such as annual fescues (Vulpia spp.). Both may occur in waste areas. Consult botanical keys for proper identification.
Relative abundance in wild: While most common in the Pacific Coast states, the species can still be hard to locate. However, it can occur in large stands, especially in vernal pools dominated by annuals. Seed retention is fair and fill is good. The period for wild collection can extend several weeks as maturation progresses along a soil moisture gradient within depressions.
Adaptation: Annual hairgrass reaches its preeminence in vernal pools, mudflats and other shallow depressions that are ponded in winter and desiccated in summer. In California, habitat also includes alkali and coastal grasslands, the edges of alkali playas, and seasonally or periodically inundated wetlands dominated by annuals. Other habitats can include streambanks, roadsides, drier banks, vernal seepage areas, waste areas, and mountain meadows. Typical substrates appear to be acidic (pH 5) to moderately alkaline fine textured clay soils and silt loams above a shallow, impervious layer. However, it also grows on coarse textured substrates that stay moist through seed development. Annual hairgrass apparently tolerates some salinity and prefers full sun. Fall germinants actively grow all winter, tolerating several days to several weeks of continual submergence.