Flower:

A single thick spike 4 to 6+ inches long at the tip of the stem, usually nodding and usually with 2 ascending spikelets (flower clusters) at each node, rarely 3. Each spikelet is 10 to 20 mm long (excluding awns) and usually has 2 or 3 florets, rarely 4; the uppermost floret may be sterile. Color is commonly light green at flowering time.

At the base of a spikelet is a pair of bracts (glumes), both firm, rough-textured, obscurely 2 or 3-veined, more or less linear tapering at the tip to a straight awn, 14 to 30 mm (to 1+ inch) long including the awn, .5 to .8 mm wide, the base somewhat hardened, slightly narrowed or not, straight to slightly bowed, the pair of glumes spreading away from the stem. Florets are surrounded by a pair of bracts (lemma and palea), the lemma usually minutely hairy, 5 to 7-veined, the body 7 to 14 mm long with a straight awn 9 to 33 mm long; the palea is somewhat shorter than the lemma, 2-veined, hairless.

Leaves and stems:

The 5 to 10 leaves are alternate, up to 10 inches long, 8 to 15+ mm (to ½ inch) wide, flat, arching to floppy, fairly evenly distributed along the stem, hairless though may be rough-textured, and commonly twisted near the base so the underside faces up. Color is dull green.

The sheath is hairless except for a fringe of short hairs along the edge, and usually has a pair of small brown to purplish lobes (auricles) at the apex. The ligule (membrane where the leaf joins the sheath) is less than 1 mm long, more or less straight across, and lacks a fringe of hairs. Nodes are hairless and usually most are hidden in the sheaths. Stems are unbranched, smooth, erect to ascending, multiple from the base, forming loose to dense clumps.

Fruit:

The awns typically remain relatively straight as spikelets mature, all turning a light brown when dry. Florets drop off individually as they mature, leaving the glumes behind on the stalk. Grains (seeds) are elliptic, purplish-brown, and have a tuft of white to light brown hairs at the tip.

Notes:

There are 10 Elymus species in Minnesota (not counting vars/subspecies); Riverbank Wild Rye is uncommon in the state, with scattered populations in a handful of counties. It is found primarily on or near shady river and stream banks or wetland margins, often in sandy soils.

Elymus riparius is distinguished by its leafy stems; sheaths hairless except for a fringe of short hairs along the edge; glumes less than 1 mm wide, 14 to 30 mm long, about equal in length and not (much) bowed at the base; nodding spike with straight awns; spikelets paired at the nodes, usually with 2 or 3 florets; lemmas minutely hairy or rough-textured. Rarely spikelets are 3 at a node, or have 4 florets.

There are several Elymus species with nodding spikes that may be confused with E. riparius: Interrupted Wild Rye (Elymus diversiglumis) has glumes that are distinctly unequal in length and less than .5 mm wide; Wiegand's Wild Rye (Elymus wiegandii) is taller (to 6 ft) and leafier (9 to 16 leaves), with a larger spike that is distinctly drooping from near the base; Canada Wild Rye (Elymus canadensis) has widest glumes at least 1 mm wide; Silky Wild Rye (Elymus villosus) has hairy leaves and sheaths, 1-flowered spikelets, and longer hairs on lemmas. E. riparius is known to hybridize with several other Elymus species, though none of its hybrids have been identified in Minnesota.