Flower:

Raceme-like branching cluster 3 to 12 inches long at the tip of the stem, the 4 to 15 main branches appressed to ascending, with 1 to several appressed branchlets per branch, each branchlet up to about 3/8 inch (1cm) long. Spikelets (flower clusters) are about 1/8 inch (2 to 3.5mm) long, flattened, round to broadly oval with an abruptly pointed tip, and have a single fertile floret, occasionally also with a single, minute, sterile floret. Spikelets are arranged on one side of the rachis (stalk), tightly packed in 2 rows, the spikelets overlapping. All parts are hairless.

At the base of a spikelet is a pair of bracts (glumes) that are firm, light green with thin translucent edging, D-shaped in outline, pointed at the tip, 3-veined, both the same size and the pair completely enclosing the floret except the very tip. Surrounding a floret are a pair of bracts (lemma and palea), the lemma lance-elliptic, tapering to a pointed tip, 5-veined and as long as or slightly longer than the glumes. The palea is slightly shorter than the lemma and 2-veined.

Leaves and stems:

Leaves are 3 to 8 inches long, 1/8 to 3/8 inch (4 to 10mm) wide, flat, the surfaces hairless but rough textured. Sheaths are hairless with thin, translucent white edging, and mostly overlap near the tip. Basal leaves are few. The ligule (membrane where the leaf joins the sheath) is a loose, thin, membranous band up to about 3/8 inch (3 to 11mm) long, triangular or ragged along the edge, and often folded back. Nodes are hairless and green to purplish. Stems are erect, hairless, single or a few from the base, forming loose clumps.

Fruit:

Spikelets ripen to light brown, the spikelets shedding as each grain matures, leaving a naked stem behind. Grains (seeds) are light to medium brown and less than 2 mm long.

Notes:

American Slough Grass is a common grass of open, wet places and is native to both North America and Asia. Its unique spikelet shape and arrangement are distinctive. Note that other references state the ligules are hairy, but this was not an obvious trait.