Agrostis hyemalis is a perennial, C3 grass (Waller and Lewis 1979), 30-90 cm tall, tufted.
Leaves alternate, small, below middle of stem, mostly basal, 0.1-0.2 cm wide, erect, narrow, often rolled inward; ligule about 0.2 cm.
Flower spikelets 1-flowered, about 0.2-0.3 cm long, shiny, in small dense clusters at ends of branches; inflorescence purplish, diffuse, open, wide spreading, often half as long as plant; branches wiry, rough textured, branching again near ends; blooming and fruiting May-June; stems break off, dispersing seeds like tumble weed.
Wetland status: FAC.
Frequency in NYC: Infrequent.
Habitat: Open areas, burns, open fill, soil pH 5-7.5, tolerant of anaerobic soils and fire; moderately tolerant of salt and shade; intolerant of drought (USDA, NRCS 2006).
Notes: Often infected with symbiotic endophytic fungi Acremonium sp. and/or Epichloë amarillans (Clavicipitaceae), (Clay and Leuchtmann 1989; Schardl and Leuchtmann 1999).