Variable tufted glabrous perennial, culms slender or more commonly robust, 15–150 cm high. Leaf-blades more or less scabrous, flat or loosely inrolled, to 30 cm long and 9 mm wide; ligules obtuse, often toothed, 1.5–7 mm long. Inflorescence typically a dense cylindric panicle, occasionally lobed near base, or sparse and interrupted, to 18 cm long. Spikelets (3–)c. 5(–6) mm long, green or purplish; lower glume slightly to considerably longer than upper, both acute to acuminate, keeled, scabrous along the keel; lemma oblong to narrow-lanceolate, generally c. three-quarters as long as spikelet, shortly 4-toothed at apex, minutely scabrous, awned within the lower third or rarely from near midway; awn usually distinctly exceeding spikelet, twisted in lower part; callus hairs to c. 1 mm long; rachilla bristle not produced. Flowers Oct.–May.
LoM, MuM, Wim, GleP, Brid, VVP, VRiv, MuF, GipP, OtP, WaP, Gold, CVU, GGr, DunT, NIS, EGL, EGU, WPro, HSF, HNF, OtR, Strz, MonT, HFE, VAlp. Also WA, SA, NSW, ACT, Tas. The most widespread and variable Deyeuxia in Victoria, usually occurring in poorly drained areas within a wide range of vegetation types, but not in tall forests or high-alpine situations.
Vickery (1940) briefly circumscribed eight forms of D. quadriseta without erecting formal names for them, and formally recognized var. cylindrica (R. Br.) Vickery, apparently confined to WA. Subsequent workers have not validated any of Vickery's forms and likewise var. cylindrica is generally not maintained.
A noteworthy variant, however, and one probably warranting formal recognition, has been recorded from south-west Victoria (e.g. Otway Ranges, Portland area). It has rather weak, slender culms, flaccid leaves and narrow, depauperate panicles with very small spikelets (barely 3 mm).
