Flower:

A single erect spike 2 to 8 inches long at the tip of the stem, usually with a single spikelet (flower cluster) at each node, rarely 2, the spikelets appressed to slightly ascending and usually more than twice as long as the space between nodes (internodes). Spikelets are flattened, the flat side pressed against the stem, and arranged alternately on opposite sides of the stem, 10 to 25 mm long (excluding any awns) and have 4 to 7 florets; the uppermost floret may be sterile.

At the base of a spikelet is a pair of bracts (glumes), both thin and translucent along the edges on the tip half, 3 to 6-veined, keeled at least on the tip half, hairless but rough along the keel, lance-elliptic, pointed at the tip, with or without a straight awn to 3 mm long, the body 7 to 12 mm (to ~½ inch) long. Florets are surrounded by a pair of bracts (lemma and palea), the lemma hairless, 5 to 7-veined, the body 8 to 12 mm long, with or without a straight awn .2 to 4 mm long, occasionally up to 10 mm; the palea is nearly as long as the lemma, 2-veined, finely hairy along the keels. Stamen tips (anthers) are 3 to 7 mm long. The stalk between florets (rachilla) and the hardened base of the floret (callus) are hairless.

Leaves and stems:

The 3 to 5 leaves are alternate, ascending, up to 12 inches long, up to 10 mm (3/8 inch) wide, mostly flat and stiff, usually with a few hairs along the veins on the upper surface. The sheath is hairless to variously hairy, and has a pair of small green to brown lobes (auricles) at the sheath apex. The ligule (membrane where the leaf joins the sheath) is up to 1.5 mm long, more or less straight across, and lacks a fringe of hairs. Nodes are hairless. Stems are unbranched, smooth, usually erect, single or a few from the base, and can form large colonies from long creeping rhizomes. The whole plant is sometimes covered in a waxy bloom (glaucus) giving a blue-green cast.

Fruit:

The awns remain straight as spikelets mature, all turning straw-colored to bleached tan when dry. Florets do not easily separate from the spikelet; the entire spikelet drops off at maturity leaving a naked stem behind. Grains (seeds) are elliptic with a tuft of white hairs at the tip.

Notes:

There are 10 Elymus species in Minnesota (not counting vars/subspecies); Quackgrass, introduced from Eurasia and formerly known as Agropyron repens or Elytrigia repens, is one of the most common in the state and considered one of the most common weeds on the planet. While it readily takes hold in disturbed soils such as roadsides, gardens and farm fields, it can invade higher grade habitat as well and can be problematic in prairies, savannas and rock outcrops. Its long rhizomes and fibrous root system can form dense mats a few inches below the surface, which can inhibit the growth of other plants. Before the days of glyphosate, it was a major agricultural pest.

Elymus repens is distinguished by its slender, erect spike; appressed spikelets usually single (rarely 2) at the nodes and fairly crowded on the stem, the space between nodes (internodes) usually 3 to 7 mm; 4 to 7 florets per spikelet; anthers more than 2.5 mm long; both glumes about equal in size, thin and papery along the edges on the tip half; florets not easily separated from the spikelet at maturity, the entire spikelet including glumes dropping off; leaves firm, usually straight, hairless or with a few hairs, the widest leaves 6 to 10 mm. Glumes and lemmas lack awns or have straight awns usually less than 5 mm long, rarely as long as 10 mm.

Quackgrass might be confused with several other species, but most strongly resembles Slender Wheatgrass (Elymus trachycaulus subsp. trachycaulus), which is clump-forming and weakly rhizomatous at best, though clumps are frequently loose and not obvious. Slender Wheatgrass spikes tend to be more widely separated (internodes more than 7 mm long), the florets are easily removed from the spikelet, the rachilla and callus are usually hairy, anthers are less than 2.5 mm long, and leaves are up to 6 mm wide.

Other awnless or short-awned Wheatgrasses, all of which have flattened spikelets single at the nodes with the flat side facing the stem, include Crested Wheatgrass (Agropyron cristatum), which has crowded spikelets that are spreading/ascending, long appressed hairs on the rachis (spike central stalk) and spikelet stalks; Western Wheatgrass (Pascopyrum smithii), which has strongly blue-green leaves with strongly raised veins; Intermediate Wheatgrass (Thinopyrum intermedium), which has blunt-tipped glumes and lemmas and leaves with strongly raised veins. Somewhat similar are the Ryegrasses (Lolium species), which also have flattened spikelets single at the nodes, but they are rotated so the spikelet edge, not the flat side, is against the stem.