Elymus trachycaulus (Slender Wheatgrass)

Plant Info
Also known as:
Genus:Elymus
Family:Poaceae (Grass)
Life cycle:perennial
Origin:native
Habitat:part shade, sun; average to dry sandy or rocky soil; prairies, savanna, dunes, shores, forest openings, rocky slopes, rock outcrops
Fruiting season:July - August
Plant height:1 to 5 feet
Wetland Indicator Status:GP: FACU MW: FACU NCNE: FACU
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: indistinct Cluster type: spike

[photo of spike] A single erect spike 2 to 10 inches long at the tip of the stem, usually with a single spikelet (flower cluster) at each node, rarely 2, the spikelets appressed to the stem and usually at least twice as long as the space between nodes (internodes) though this is quite variable. Spikelets are flattened, the flat side pressed against the stem, and arranged alternately on opposite sides of the stem or somewhat on the same side, 9 to 17 mm long (excluding any awns) and have up to 9 florets, mostly 3 to 5; the uppermost floret may be sterile.

[close-up of spikelet, subsp. trachycaulus] At the base of a spikelet is a pair of bracts (glumes), both thin and translucent along the edges, 3 to 7-veined, asymmetrically keeled, hairless but rough along the keel, lance-elliptic, pointed at the tip, with or without a straight awn to 11 mm long, the body 5 to 17 mm (to 2/3 inch) long, 1.8 to 2.3 mm wide. Florets are surrounded by a pair of bracts (lemma and palea), the lemma hairless, 5 to 7-veined, rough along the veins, sometimes fringed with short hairs along the edges, the body 6 to 13 mm long usually with a straight awn up to 40 mm (~1½ inch) long; the palea is about as long as the lemma, 2-veined. Stamen tips (anthers) are 1 to 2.5 mm long. The stalk between florets (rachilla) and the hardened base of the floret (callus) are frequently covered in white hairs up to .4 mm long.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of sheath, ligule and node] Leaves are alternate, ascending, mostly on the lower stem, up to 6 mm (¼ inch) wide, mostly flat, sometimes rolled along the edge (involute), usually hairless, occasionally hairy on the upper surface. The sheath is usually hairless with the lower sheaths sometimes sparsely hairy, and may or may not have a pair of small brown to purplish lobes (auricles) at the sheath 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. Stems are unbranched, smooth, usually erect, single or multiple from the base forming loose to tight clumps, and may form loose colonies from short rhizomes.

Fruit: Fruit type: seed without plume

[photo of mature floret and grain] The awns remain straight as spikelets mature, all turning straw-colored to bleached tan when dry. Florets readily separate from the spikelet and drop off individually as they mature; the glumes may or may not also drop off. 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); Slender Wheatgrass, formerly known as Agropyron trachycaulum, is one of the more common in the state and also the most variable, particularly in the glume venation and awn lengths of both glumes and lemmas. It is found in a variety of habitats, including prairies, jack pine forest, beaches, dunes, river banks, grassy slopes, cliffs, rock outcrops and the occasional roadside, usually in dry soil, less often in wet depressions and swamp margins.

Elymus trachycaulus is distinguished by its slender, erect spike; appressed spikelets usually single (rarely 2) at the nodes and not crowded on the stem, the space between nodes (internodes) at mid-spike usually 7 mm or more; 3 to 5(9) florets per spikelet; anthers less than 2.5 mm long; both glumes nearly equal in size, 1.8 to 2.3 mm wide, thin and papery along the edges; lemma rachilla and callus usually hairy; florets easily separated at maturity, glumes may persist on the stem; leaves firm, usually straight, usually hairless, up to 6 mm wide. There are 2 subspecies in Minnesota: subsp. subsecundus (formerly Agropyron subsecundum) has long-awned glumes and lemmas (awns to 11 mm and 17 to 40 mm respectively) and spikes can appear to be somewhat 1-sided; subsp. trachycaulus has glume awns absent or up to 2 mm long, lemma awns less than 5 mm. A third subsp. (virescens) is restricted to Greenland. E. trachycaulus is considered clump-forming, though often loosely so and may appear more colony-forming than clump-forming, which is how we've usually encountered it.

While subsp. subsecundus is fairly easily recognizable from the long awns, spikelets single at the nodes and the spike almost appearing 1-sided, subsp. trachycaulus might be confused with several other species, but most strongly resembles Quackgrass (Elymus repens). Quackgrass is rhizomatous (not clump-forming), spikelets tend to be crowded together (internodes mostly less than 7 mm long), the florets are not easily removed from the spikelet, the rachilla and callus are hairless, anthers are more than 2.5 mm long, and leaves are up to 10 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.

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More photos

Photos by K. Chayka taken in St. Louis County and in Wisconsin. Photos by Peter M. Dziuk taken in Fillmore, Otter Tail and Pope Counties, and in Wisconsin. Elymus trachycaulus clump by Matt Lavin, via Wikimedia Commons, used under CC BY-SA 2.0

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