Plants annual. Culms 80-110 cm, erect. Lower sheaths with dense, soft, appressed hairs; ligules 1-1.5 mm, hairy, obtuse, erose; blades 10-20 cm long, 2-6 mm wide, coarsely pilose on both surfaces. Panicles 11-30 cm long, 4-20 cm wide, open, erect or nodding; branches usually longer than the spikelets, ascending to widely spreading, slender, slightly curved or straight. Spikelets 10-25 mm, lanceolate, terete to moderately laterally compressed, often purple-tinged; florets 4-10, bases concealed or visible at maturity; rachilla internodes concealed or visible at maturity. Glumes glabrous; lower glumes 4-6 mm, 3-veined; upper glumes 5-8 mm, 5-veined; lemmas 7-9 mm long, 1.1-1.5 mm wide, lanceolate, obscurely 7-veined, rounded over the midvein, glabrous, coriaceous, margins slightly angled, inrolled or not at maturity, apices acute, bifid, teeth shorter than 1 mm; awns 6-11 mm, straight, arising at varying distances below the lemma apices; anthers 2.5-5 mm. Caryopses shorter than the paleas, weakly to strongly inrolled. 2n = 14.
Conn., N.J., N.Y., Wash., Del., D.C., Wis., W.Va., Mass., Maine, N.H., R.I., Vt., Fla., Wyo., N.Mex., Tex., La., Tenn., N.C., S.C., Pa., Nev., Va., Colo., Md., Calif., Ala., Kans., N.Dak., Nebr., Okla., S.Dak., Miss., Ark., Ill., Ga., Ind., Iowa, Ariz., Idaho, Alta., B.C., Man., Ont., Que., Sask., Mont., Oreg., Ohio, Utah, Mo., Minn., Mich., Ky.
Bromus arvensis grows along roadsides and in fields and waste places at scattered locations in the Flora region. It is native to southern and south-central Europe.
"decumbent" is not a number.