Plants perennial; loosely cespitose or the culms solitary; rhizomes elongate 0.7–2 mm thick. Culms 40–85 (110) cm tall. Sheathsbrownish or reddish; ligules 2.5–5.5 mm long; blades of basal and cauline leaves 2.5–5.5 mm wide, abaxial surface glabrous and shiny, adaxial surface pilose; blade of flag leaf 1–4.5 (6) cm long, 3–4.5 mm wide. Panicles (5)7–.5–15 cm long, 2–10 cm wide, open, pyramidal, with 20–100+ spikelets; branches with 3+ spikelets. Spikelets 4–6.3 mm long, tawny at maturity; rachilla internodes0.1–0.3 mm long. Glumes subequal, exceeding the florets, glabrous, often somewhat purplish; lowest 2 florets staminate; lowest 2 lemmas 3–5 mm long, with hairs to 0.5 mm long towards their tips, margins with 16–30 hairs per mm, hairs 0.5–1 mm long, lemma tips acute, emarginated or bifid; lowest lemma 3–5 mm long, 1.1–1.3 mm wide, length usually less than 4 times its width, elliptic, awned, awns 0.1–1.1 mm long; bisexual lemma 2.9–3.5 mm long, hairy distally, the hairs 0.5–1 mm long, evenly distributed around the tops, their bases strongly divergent from the lemma surface; anthers of staminate florets 1.6–2.1 mm long, those of the bisexual florets 1.2–1.3 mm long. 2n = 56.
Anthoxanthum hirtum is the most widely distributed species of Anthoxanthum in North America, extending from Alaska to northeastern Quebec and south to Washington, Colorado, South Dakota, Illinois, Ohio, and New York. It is not known from Newfoundland or Greenland. Outside North America it extends from Scandinavia south to Germany and east to Asiatic Russia. It grows in wet meadows and marshes with sweet, not salty or brackish, water.Because much of its native habitat has been drained, it is becoming less common. It does not grow well from seed.
Its short flag leaf and more circular spikelets distinguish it from A. occidentale. The relative abundance and even distribution of hairs longer than 0.5 mm on the bisexual lemma distinguish it from A. nitens.
Weimark (1971, 1987) has recognized three subspecies in A. hirtum, which he treated as Hierochloë hirta. He stated that only subsp. arctica grew in North America but several North American specimens seem to fit within his circumscription of H. hirta subsp. hirta. Because the variation between the two appears continuous, North American plants are regarded here as belonging to A. hirtum (Schrank.) Y. Schouten & Veldkamp subsp. hirtum