Calamagrostis montanensis (Plains Reedgrass)

Plant Info
Also known as:
Family:Poaceae (Grass)
Life cycle:perennial
  • State Special Concern
Habitat:sun; dry sandy or gravelly soil; prairies, savannas
Fruiting season:June - July
Plant height:6 to 20 inches
Wetland Indicator Status:none
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: panicle Cluster type: spike

[photo of flowering panicle] A panicle at the tip of the stem 1½ to 4 inches long, narrowly pyramidal in outline at flowering time with erect to ascending branches less than 1½ inches long, the branches becoming mostly erect at maturity. Spikelets (flower clusters) are somewhat crowded along a branch, somewhat compressed, 3 to 5 mm (less than ¼ inch) long, yellowish often with a purple tinge, and have a single floret.

[close-up of spikelet] At the base of a spikelet is a pair of bracts (glumes), both awnless, keeled and 1-veined, smooth to rough-textured, tapering to a sharply pointed tip, 3 to 5 mm long, as long as the spikelet. Florets are surrounded by a pair of bracts (lemma and palea), the lemma thin, 2.5 to 4 mm long, somewhat shorter than the upper glume, notched with 4 teeth at the tip, and have a straight to bent awn arising from the lower third of the back (rarely above the middle) that sometimes extends beyond the tip of the lemma; the palea is somewhat shorter than the lemma. The thickened base of the floret (callus) is densely covered in straight, white hairs that are more or less half as long as the lemma; a stalk (rachilla) also covered in long hairs extends about 1 mm above the callus.

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

[photo of sheaths, ligules and involute leaves ©Matt Lavin] Leaves are erect to ascending, basal with 1 or 2 alternate stem leaves, 1 to 3 mm (to 1/8 inch) wide, 2 to 8 inches long, hairless but rough on both surfaces, usually rolled in along the edges (involute), and green to blue-green. The sheath is hairless. The ligule (membrane where the leaf joins the sheath) is 2 to 4 mm long, ragged or shredded along the tip edge and lacks a fringe of hairs. Nodes are smooth. Stems are erect, hairless but rough-textured, unbranched, usually single, sometimes a few from the base. Loose clumps are formed from a mix of flowering and vegetative shoots, and loose colonies may also form from long rhizomes.

Fruit: Fruit type: seed without plume

[photo of mature florets] At maturity, branches become mostly 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, about 1.5 mm long.


Plains Reedgrass is a common grass of the northern Great Plains but is rare in Minnesota, where it reaches the eastern edge of its range. According to the DNR, it's noted as a short grass that may exist mostly vegetatively, not sending up flowering stems except where competition is sufficiently reduced, such as on old gopher mounds. Much of the short-grass prairie needed for this species to thrive, which was already in short supply pre-European settlement, has been plowed up for agriculture or degraded by grazing. It was listed as a Special Concern species in 1996 due to the limited amount of suitable habitat and limited number of populations in the state. We encountered it in a remnant prairie strip between an agricultural field and a gravel road, which was subject to some mowing (thus had shorter than average stems) but still intact and relatively weed-free (thanks for the location, Otto!).

Plains Reedgrass is recognized by its dry sandy or gravelly habitat; short stature, usually 8 to 16 inches tall, rough stems mostly single; only 1 or 2 stem leaves, usually 2 to 3 mm wide, rough, green to blue-green, with in-rolled edges; terminal panicle (spike-like at maturity) of 1-flowered spikelets 3 to 5 mm long; both glumes hairless, awnless, equal in size and shape, longer than the floret; callus and rachilla covered in long, straight hairs, callus hairs half or so as long as the lemma; lemmas 4-toothed at the tip; lemma awns usually arising from the lower third of the back, usually slightly to strongly bent, not usually extending beyond the tip of the lemma.

Similar species are the related Slimstem Reedgrass (Calamagrostis stricta subsp. stricta), which is found in wetter habitats such as fens and wet prairies, and Purple Reedgrass (Calamagrostis purpurescens), which is only found in northern Cook County on moss and lichen-covered cliffs, and has finely hairy leaves. At a glance Plains Reedgrass may be confused with June Grass (Koeleria macrantha) which has hairy sheaths, spikelets usually have 2 florets, lemmas lack long hairs on the callus and rachilla and are rarely awned, and flowering stems are more typically numerous in a tight clump, though we have encountered them single (and short) on occasion, which was the cause of much frustration on our part.

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More photos

Photos by K. Chayka taken in Polk County. Photos by Peter M. Dziuk taken in North Dakota. Photos by Otto Gockman taken in Polk County. Sheaths, ligules and leaves by Matt Lavin, via Wikimedia Commons, used under CC BY-SA 2.0.


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