Plants annual or perennial. Culms 8-200 cm, erect or decumbent. Sheaths open; auricles absent; ligules membranous; blades usually flat, sometimes involute, lax. Inflorescences panicles, diffuse, sometimes 1-sided. Spikelets 15-50 mm, laterally compressed, with 1-6(8) florets; rachillas not prolonged beyond the uppermost floret; disarticulation above the glumes, usually also between the florets, or cultivated forms not disarticulating. Glumes usually exceeding the florets, membranous, glabrous, 3-11-veined, acute; calluses rounded to pointed, with or without hairs; lemmas usually indurate and enclosing the caryopses at maturity, 5-9-veined, often with twisted, strigose hairs below midlength, apices dentate to bifid or biaristate, awns (if present) dorsal, usually once-geniculate and strongly twisted in the basal portion; paleas bifid or entire, ciliate on the keels; lodicules 2, free, glabrous, toothed or not toothed; anthers 3; ovaries hairy. Caryopses terete, ventrally grooved, pubescent; hila linear. x = 7. Name from the Latin avena, oats.

Avena, a genus of 29 species, is native to temperate and cold regions of Europe, North Africa, and central Asia; it has become nearly cosmopolitan through the cultivation of cereal oats and the inadvertent introduction of the weedy species. Six species have been introduced into the Flora region.

Reports of Avena strigosa Schreb. from California are based on misidentifications. The specimens involved belong to Avena barbata.

1.   Avena barbata Pott ex Link
Slender Oats, Slender Wild Oats

Plants annual. Culms 60-80(150) cm, initially prostrate, generally becoming erect. Sheaths of the basal leaves pilose, distal sheaths usually glabrous; ligules 1-6 mm, obtuse; blades 6-30 cm long, 2-20 mm wide, glabrous or pilose. Panicles 15-35.5(50) cm long, 6-12 cm wide, erect or nodding. Spikelets 21-30 mm, with 2-3 florets; disarticulation beneath each floret; disarticulation scars elliptic to triangular. Glumes subequal, 15-30 mm, 7-9-veined; calluses bearded, hairs 2-3 mm; lemmas 15-26 mm, densely strigose below midlength, apices acute, biaristate, veins extending 2-4 mm beyond the apices, awns 30-45 mm, arising about midlength, geniculate; lodicules narrowly triangular, without lobes on the wings; anthers 2.5-4 mm. 2n = 28.

Avena barbata is native to the Mediterranean region and central Asia. It has become naturalized in western North America, particularly California, displacing native grasses It was collected once in Vancouver, British Columbia, but should be considered a waif there..

2.   Avena fatua L.
Wild Oats, Folle Avoine

Plants annual. Culms 8-160 cm, prostrate to erect when young, becoming erect at maturity. Sheaths of the basal leaves with scattered hairs, distal sheaths glabrous; ligules 4-6 mm, acute; blades 10-45 cm long, 3-15 mm wide, scabridulous. Panicles 7-40 cm long, 5-20 cm wide, nodding. Spikelets 18-32 mm, with 2(3) florets; disarticulation beneath each floret; disarticulation scars round to ovate or triangular. Glumes subequal, 18-32 mm, 9-11-veined; calluses bearded, hairs to 1/4 the length of the lemmas; lemmas 14-22 mm, usually densely strigose below midlength, varying to sparsely strigose or glabrous, veins not extending beyond the apices, apices usually bifid, teeth 0.3-1.5 mm, awns 23-42 mm, arising in the middle 1/3 of the lemmas; lodicules without lobes on the wings; anthers about 3 mm. 2n = 42.

Avena fatua is native to Europe and central Asia. It is known as a weed in most temperate regions of the world; in some parts of Canada and the United States it is considered a noxious weed.

Avena fatua is sometimes confused with A. occidentalis, but differs in having shorter, wider spikelets, fewer florets, and a distal floret which does not have a heart-shaped disarticulation scar. Hybrids between A. fatua and A. sativa are common in plantings of cultivated oats. The hybrids resemble A. sativa, but differ in having the fatua-type lodicule; some also have a weak awn on the first lemma. They are easily confused with fatuoid forms of A. sativa.

3.   Avena hybrida Peterm.

Plants annual. Culms erect; nodes often pubescent. Sheaths glabrous; ligules 4-5 mm, obtuse or acute; blades 12-25 cm long, 7-12 mm wide. Panicles 15-30 cm, equilateral, sometimes slightly secund. Spikelets 15-24 mm, with 2-4 florets; disarticulation beneath each floret; disarticulation scars oval to round, those on the third (and sometimes the second) floret(s) heart-shaped. Glumes equal, 15-22 mm, 7-9(11)-veined; calluses bearded; lemmas about 21 mm, usually glabrous, sometimes pubescent beneath the awn insertion, irregularly bidenticulate to bisubulate, veins not extending beyond the apices, awns about 30 mm, arising at midlength; lodicules with a small side lobe; anthers about 2 mm. 2n = 42.

Avena hybrida is native to western and central Asia; it grows as a weed in Europe. It has been reported from Essex County, Massachusetts, and Prince Edward Island.

4.   Avena occidentalis Durieu
Western Oats

Plants annual. Culms 50-80 cm, erect. Sheaths glabrous or sparsely pubescent, hairs 0.5-1 mm, sometimes confined to the margins; ligules of the lower leaves 3-5 mm, those of the upper leaves 1.5-2.5 mm, acute; blades 12-25 cm long, 5-11 mm wide. Panicles 15-26 cm. Spikelets 30-40 mm, with 3-4(5) florets; disarticulation beneath each floret; disarticulation scars of the lower florets round to elliptic, those of the third and fourth florets heart-shaped. Glumes subequal, 30-40 mm, 7-9-veined; calluses bearded, hairs 3-5 mm; lemmas 14-26 mm, usually densely strigose below midlength, varying to sparsely strigose or glabrous, veins not extending beyond the apices, apices bifid, teeth sometimes shortly aristate, awns arising at midlength; lodicules without lobes on the wing; anthers 2-3.2 mm. 2n = 42.

Avena occidentalis is native to the Canary Islands, coastal North Africa, and Saudi Arabia; it is now established in western North America from Oregon to northern Mexico. It is often confused with A. fatua, but differs in its longer, narrower spikelets, greater number of florets, and the heart-shaped disarticulation scars of the distal florets.

5.   Avena sativa L.
Oats, Cultivated Oats, Naked Oats, Avoine

Plants annual. Culms 40-180 cm, prostrate to erect when young, becoming erect at maturity. Sheaths smooth or scabridulous; ligules 3-8 mm, acute; blades 8-45 cm long, 3-14 (25) mm wide, scabridulous. Panicles (6)20-40 cm long, 5-15 cm wide, nodding. Spikelets(18)25-32 mm (to 50 mm in naked oats), with 1-2 florets (to 7 in naked oats); disarticulation not occurring, the florets remaining attached even when mature. Glumes subequal, (18)20-32 mm, 9-11-veined; calluses glabrous; lemmas 14-18 mm, usually indurate (membranous in naked oats), usually glabrous, sometimes sparsely strigose, apices erose to dentate, longest teeth 0.2-0.5 mm, awns usually absent, 15-30 mm when present, arising in the middle 1/3, weakly twisted, not or only weakly geniculate; lodicules with a lobe or tooth on the wings, this sometimes very small; anthers (1.7)3-4.3 mm. 2n = 42.

Avena sativa, a native of Eurasia, is widely cultivated in cool, temperate regions of the world, including North America. Fall-sown oats are planted in the Pacific and southern states in United States; spring-sown oats are more important elsewhere in North America. It is sometimes planted as a fast-growing soil stabilizer along roadsides. Several forms are grown, of which the most distinctive are naked oats. These differ from typical forms as indicated in the description and in having caryopses that fall from the florets. Escapes from cultivation are common but rarely persist.

Avena sativa hybridizes readily with A. fatua. The hybrids are easily confused with fatuoid forms of A. sativa, which differ in having the sativa-type lodicule.

6.   Avena sterilis L.
Animated Oats, Avoine Stérile

Plants annual. Culms 30-120 cm, initially prostrate, becoming erect at maturity. Sheaths glabrous or hairy; ligules 3-8 mm, acute to truncate-mucronate; blades 8-60 cm long, 4-18 mm wide, scabridulous, often ciliolate on the margins. Panicles 10-45 cm long, 5-25 cm wide. Spikelets 24-50 mm, with 2-5 florets; disarticulation beneath the basal floret, the florets falling as a unit; disarticulation scar oval to round-elliptic. Glumes subequal, 20-50 mm, 9-11-veined; calluses bearded, hairs to 1/5 the length of the lemmas; lemmas 17-40 mm, usually densely strigose below midlength, varying to sparsely strigose, glabrous, or scabridulous, apices bidentate to bisubulate, teeth 1-1.5 mm, awns 30-90 mm, arising in the middle 1/3; lodicules without a lobe on the wing; anthers 2.5-4 mm. 2n = 42.

Avena sterilis is native from the Mediterranean region to Afghanistan; it now grows on all continents. It has become naturalized in California and Oregon, where it can be found in fields, vineyards, orchards, and on hillsides. It is listed as a noxious weed by the U. S. Department of Agriculture.