Flower:

Flowering head is an open panicle 4 to 8 inches long, typically nodding to one side, the branches arching, drooping at the tips with 2 or more spikelets (flower clusters) per branch. Spikelets are stalked, oblong-elliptic in outline, not much flattened, 15 to 35+ mm (to 1 3/8+ inch) long, with 7 to 15 fertile florets. One or more sterile florets may be at the tip.

At the base of a spikelet is a pair of bracts (glumes), both hairless and pointed at the tip, the lower glume 4 to 5 mm long and (3)5-veined, the upper glume 6 to 8 mm long and 7-veined. Surrounding a floret is a pair of bracts (lemma and palea). Lemmas are elliptic to somewhat kite-shaped, 8 to 13 mm long, hairless to minutely hairy, weakly 7-veined, notched at the tip forming 2 teeth with a straight awn 5 to 16 mm (to 2/3 inch) long arising between the teeth, more than 1.5 mm below the tip of the lemma, the lowest lemma on a spikelet with the shortest awn and the longest awn twice or more that length. The palea is 1 to 2.5 mm shorter than the lemma, elliptic, 2-veined with sparse, long hairs along the veins. Sterile florets are like the fertile but underdeveloped.

Leaves and stems:

Leaf blades are spreading to ascending, flat, 2 to 6 inches long, 3 to 6 mm (to ¼ inch) wide, hairy with sparse to moderate long, spreading or crinkly hairs.

Sheath edges are fused for most of their length (a closed sheath), densely covered in long, downward pointing (retrorse) hairs, the hairs often more crinkly near the sheath tip. The ligule (membrane where the leaf joins the sheath) is membranous, 1 to 2 mm long, jagged along the top edge and lacks a fringe of hairs. Nodes are hairy or not. Stems are hairless or hairy just at the nodes, a few to several from the base forming clumps, erect to ascending or spreading from the base and rising at a lower node (geniculate). 

Fruit:

Florets mature to light brown, the awns spreading out away from the spikelet as they dry, sometimes becoming curled, and each floret dropping off individually leaving the glumes persisting on the stalk.

Grains are somewhat flattened, elliptic, 5 to 6 mm long, and have a bundle of white hairs at the tip.

Notes:

Bromes are cool season grasses (optimal growth below 75°), usually clump-forming, have closed sheaths, panicles that are often drooping or nodding to one side, multi-flowered spikelets, unequal glumes, and lemmas that are typically awned, hairy and usually notched at the tip forming 2 teeth with the awn arising between the teeth. The longer leaves also frequently twist from near the base so the underside and upperside are flipped. Most Bromes found in Minnesota have sheaths and nodes that are hairy to various degrees and are mostly distinguished by the number of veins on the glumes, length of the lemma awns, and sometimes leaf characteristics.

Japanese Brome, sometimes included in Bromus arvensis, is one of two weedy (and potentially invasive) annual Bromes in Minnesota, the other being Cheatgrass (Bromus tectorum). Besides being an annual, Japanese Brome is distinguished by densely hairy sheaths, leaves sparsely to moderately covered in long spreading or crinkly hairs, ligule 1 to 2 mm long, 7 to 15 florets per spikelet, a (3)5-veined lower glume to 5 mm long, 7-veined upper glume to 8 mm long, mostly hairless lemmas with an awn up to 16 mm long that is at least slightly spreading at maturity, the awn of the lowest lemma in a spikelet about half the size of the longest awn, palea 1 to 2.5 mm shorter than the lemma with long, sparse hairs on the veins. By comparison, Cheatgrass has fewer florets per spikelet (3 to 8), a 1-veined lower glume to 11 mm long, 3-veined upper glume to 13 mm long, longer awns (to 25mm), and usually hairier lemmas and a longer ligule (2 to 5 mm).