Flower:

Panicle 2 to 7 inches long at the tip of the stem, the branches ½ to 2+ inches long, mostly ascending at flowering time becoming appressed at maturity. Spikelets (flower clusters) are loosely overlapping to somewhat crowded along a branch, somewhat compressed, 2 to 6 mm (to ¼ inch) long, green to purple, and have a single floret.

At the base of a spikelet is a pair of bracts (glumes), both awnless, keeled, smooth to rough-textured, thick and opaque or thin and somewhat translucent at least near the tip, sharply pointed at the tip, 2 to 6 mm long, as long as the spikelet. Florets are surrounded by a pair of bracts (lemma and palea), the lemma thin, 2 to 3.5(5) mm long, usually shorter than the glumes, notched with 4 teeth at the tip, and with a straight to bent awn arising from below the middle of the back that rarely extends beyond the tip of the glumes; the palea is somewhat shorter than the lemma. The thickened base of the floret (callus) is densely covered in straight, white hairs that are half to nearly as long as the lemma; a stalk (rachilla) also covered in long hairs extends up to 1.5 mm above the callus.

Leaves and stems:

Leaves are erect to ascending, basal with 1 to 3 alternate stem leaves, 1.5 to 5.5 mm wide, 4 to 10+ inches long, flat or rolled in along the edges (involute), hairless, rough-textured to mostly smooth, and green to blue-green. The sheath is hairless, smooth to somewhat rough. The ligule (membrane where the leaf joins the sheath) is 1 to 6+ mm long, the top edge variable from pointed to straight across, may be smooth or somewhat jagged, and lacks a fringe of hairs. Nodes are smooth. Stems are erect, hairless, smooth or rough-textured, unbranched, loosely to densely clump-forming, and often form colonies from long rhizomes.

Fruit:

At maturity, branches become appressed and spikelets turn straw-colored to pale brown, the florets dropping off individually leaving the glumes behind on the stalk. Grains are brown, oblong-elliptic, about 1.5 mm long.

Notes:

Slimstem Reedgrass is a common grass of wet places across much of Minnesota but particularly in the northern half. It is salt-tolerant and may be found in calcareous, alkaline or saline soils.

Slimstem Reedgrass is recognized by its clump-forming and often colony-forming habit, stems 1 to 3 feet tall; only 2 or 3 stem leaves 1.5 to 5.5 mm wide, green to blue-green, hairless, flat or in-rolled (involute) edges; panicle of 1-flowered spikelets 2 to 6 mm long, branches ascending at flowering and appressed at maturity; both glumes hairless, awnless, equal in size and shape, longer than the floret; callus and rachilla covered in long, straight hairs, callus hairs at least half as long as the lemma but not longer; lemmas 4-toothed at the tip; lemma awns arising from below the middle of the back, straight to only slightly bent, not extending beyond the tip of the glumes.

There are 2 recognized subspecies, both of which are found in Minnesota. Subsp. stricta, the less common, is generally smaller in most characteristics; stems mostly smooth; leaves 2 to 4 mm wide, mostly involute, mostly smooth except along the edges and towards the tip; upper ligules mostly less than 3 mm long; panicle branches mostly less than 1½ inches long; glumes not usually more than 3 mm long, thin and translucent at least around the edges near the tip; lemma awn straight; callus hairs 1 to 3 mm long; stamens usually fertile. Subsp. inexpansa, much more common, is generally larger in most characteristics; stems rough-textured; leaves 3 to 6 mm wide, mostly flat, rough-textured; upper ligules mostly more than 3 mm long; longest panicle branches usually 2+ inches long; glumes usually more than 3 mm long, thick and opaque; lemma awn straight or bent; callus hairs 2 to 4 mm long; stamens often poorly developed and sterile.

There is a fair amount of overlap on many of these characteristics so multiple plants in a population should be inspected when trying to determine subspecies. The more consistent traits may be the mostly flat, rough leaves and rough stems of subsp. inexpansa vs. the relatively smooth, mostly involute leaves and smooth stems of subsp. stricta. The thick and opaque glumes vs. thin and translucent, as well as glume, lemma and hair lengths, all need further study on our part.

Similar species are the related Purple Reedgrass (Calamagrostis purpurascens) and Plains Reedgrass (Calamagrostis montanensis), both of which are found in drier habitats, and Canada Bluejoint (Calamagrostis canadensis), which is more robust with leafier stems, leaves up to 10 mm wide, and callus hairs usually about as long as the lemma. At maturity when the panicle branches are all erect, Slimstem Reedgrass may resemble a short Reed Canary Grass (Phalaris arundinacea), which has hairy lemmas that lack awns and are often shiny dark brown, leaves are 5 to 20 mm wide, and the collar (outer junction between the leaf blade and sheath) is quite prominent and often yellowish.