Flower:

Plume-like branching cluster at the top of the stem, 4 to 14 inches long, the branches erect to ascending, the whole panicle erect to nodding. Spikelets (flower clusters) are crowded on a branch, 3 to 5 mm long (excluding awns), green to dark purplish, flattened on 1 side, with 1 sterile and 1 fertile floret but appearing single-flowered.

At the base of a spikelet is a pair of bracts (glumes), the lower glume about half as long as the spikelet, pointed at the tip, the base completely wrapped around the spikelet, the upper glume as long as the spikelet, 5-veined, hairless or sparsely hairy at least along the veins, tapering at the tip to a straight awn 2 to 10 mm (to 3/8 inch) long. Surrounding a floret is a pair of bracts (lemma and palea), the lower lemma sterile and like the upper glume but the awn 10 to 60 mm (to 2+ inches) long; the lower palea is thin and about as long as its lemma. The upper lemma is fertile, as long as the upper glume or nearly so, shiny and hardened, lacks an awn, the tip thin and membranous, the edges wrapping around the edges of the similar palea.

Leaves and stems:

Leaves are alternate, to 22 inches long, 3/8 to 1 1/3 inches (10 to 35mm) wide, flat, hairless or with a few hairs on the upper surface, rough textured.

Sheaths, especially lower sheaths, are usually sparsely to moderately covered in stiff hairs, the hairs with a pimple-like base (papillose); rarely lower sheaths are hairless. The ligule (membrane where the leaf joins the sheath) is lacking, the juncture smooth and pale to purplish. Nodes are hairless to variously hairy. Stems are hairless, unbranched, mostly erect to ascending, sometimes prostrate from the base and rising at a lower node (geniculate), and are multiple from the base forming clumps.

Fruit:

The whole spikelet drops away when mature, leaving a naked stem behind. Grains (seeds) are 1.2 to 1.8 mm long, brown, and enclosed within the persistent lemma and palea.

Notes:

Walter's Barnyard Grass is a robust annual typically found along stream and river banks, on sandy shores, and in floodplains, marshes and wet meadows. Our own first encounter was in a low roadside ditch mixed in with weedy forbs, but the largest population we've seen was on the sandbars of Mississippi River backwaters.

Echinochloa is recognized by its absent ligule, (usually) awned spikelets that have 1 sterile and 1 fertile floret, and the lower glume rather shorter than the spikelet. Of the 3 Echinochloa species in Minnesota,  E. walteri is distinguished by its awned upper glumes and hairy sheaths, the hairs with pimple-like bases (papillose); occasionally sheaths are simply covered with the pimply projections and hairs are lacking, giving something of a polka-dotted look in the right light. The length of the awns can be variable even within a branch, but in our observations, lemma awns average about an inch long, much longer than the glume awns.

Of the other 2 species, Barnyard Grass (E. crus-galli) and Rough Barnyard Grass (E. muricata), both have glumes awnless or awns less than 2 mm long, and both usually have hairless sheaths.