Plants annual; tufted or culms solitary. Culms 5-120 cm, erect or geniculate, glabrous. Leaves mostly cauline; sheaths open, rounded to slightly keeled; collars glabrous, midveins continuous; auricles absent; ligules membranous, often lacerate to erose; blades flat or weakly involute, glabrous. Inflorescences terminal panicles, branches strongly ascending to divergent. Spikelets slightly laterally compressed, with 1 floret, rarely more, distal florets, if present, vestigial; rachillas prolonged as a bristle, rarely terminating in a vestigial floret; disarticulation above the glumes. Glumes unequal, lanceolate, scabrous on the upper 1/2, unawned; lower glumes 1-veined; upper glumes slightly shorter to slightly longer than the florets, 3-veined; calluses blunt, sparsely and shortly bearded or glabrous; lemmas firmer than the glumes, folded to nearly terete, obscurely 5-veined, awned from just below the apices; paleas equaling or to about 3/4 the length of the lemmas, hyaline, 2-veined; lodicules 2, free, glabrous, usually toothed; anthers 3; ovaries glabrous. Caryopses 1.2-2 mm, ellipsoidal, slightly sulcate; hila broadly ovate, 1/5 the length of the grains. x = 7. Name of uncertain origin, possibly from Greek a, not, and peros, maimed; Adanson provided no explanation.

Apera is genus of three species, native to Europe and western Asia. It is similar to Agrostis; it differs in its firm lemmas, paleas that are always present and equal or nearly so to the lemma, and prolonged rachillas. In North America, two species have been introduced, growing as weeds in lawns and disturbed ground, and in grain fields.

1.   Apera interrupta (L.) P. Beauv.
Interrupted Windgrass

Culms (5)10-50(75) cm, weak, slender, solitary or with several shoots, sometimes sparingly branched above the base; internodes usually longer than the sheaths. Sheaths often purplish; ligules 1.5-5 mm, acute to truncate, erose, margins decurrent; blades usually 4-12 cm long, 0.3-4 mm wide, flat or convolute when dry. Panicles 3-15(20) cm long, 0.4-1.5(3) cm wide, contracted, somewhat interrupted below; branches erect to ascending, most spikelet-bearing to within 2 mm of the base; pedicels 0.5-2 mm. Spikelets 2-2.8 mm, green or purplish; florets 1; rachilla extensions 0.2-0.6 mm. Lower glumes 1-2.2 mm; upper glumes 2-2.5(2.8) mm; lemmas 1.5-2.5 mm, slightly involute, awned, awns 4-10(16) mm; anthers 0.3-0.5 mm, often purplish-brown. Caryopses 1-1.5 mm. 2n = 14, 28.

Apera interrupta grows as a weed in lawns, grain fields (especially winter wheat), sandy open ground, and roadsides. Introduced from Europe, it now grows from British Columbia south to Arizona and New Mexico, as well as in Ontario and a few scattered locations in the eastern part of the Flora region.

2.   Apera spica-venti (L.) P. Beauv.
Common Windgrass, Loose Silkybent

Culms 20-80(120) cm, stout, usually with several shoots, sparingly branched; internodes shorter or longer than the sheaths. Sheaths often purplish; ligules 3-6(12) mm; blades usually 6-16(25) cm long, 2-5(10) mm wide, flat. Panicles (5)10-35 cm long, (2)3-15 cm wide, usually open, pyramidal; branches spreading, with spikelets more than 5 mm from the base, usually borne towards the ends; pedicels 1-3 mm. Spikelets 2.4-3.2 mm, often purplish; florets 1; rachilla extensions about 0.5 mm. Lower glumes 1.5-2.5 mm; upper glumes 2.4-3.2 mm; lemmas 1.6-3 mm, folded, scabridulous above the middle, awned, awns 5-12 mm; anthers 1-2 mm, greenish to yellowish, often purple-tinged. Caryopses 1-1.5 mm. 2n = 14.

Apera spica-venti grows as a weed in lawns, waste places, grain fields, sandy ground, and roadsides. Introduced from Europe, it is found in scattered locations in the Flora region.