Flower:

Erect, very slender, branching cluster 2 to 6 inches long at the top of the stem. Panicle branches are appressed with a few to several short-stalked spikelets (flower clusters) per branch. Spikelets are lance-elliptic in outline, 2.4 to 3.6 mm (to 1/8 inch) long, overlapping along a branch but not tightly crowded, and usually have a single floret, occasionally 2.

At the base of a spikelet is a pair of bracts (glumes), both thin, green to light brown, 1-veined, hairless but rough along the vein, lance to egg-shaped with a pointed tip, sometimes with an awn-like extension up to .5 mm long, the lower glume 1.2 to 3 mm long, the upper glume slightly longer than the lower glume and about ¾ as long as the spikelet. Florets are surrounded by a pair of bracts (lemma and palea), both similar in size and shape, dark green to purplish-gray, 2.5 to 3.6 mm long, pointed at the tip, the lemma 3-veined with sparse appressed hairs on the lower half or so, the palea 2-veined and hairless.

Leaves and stems:

Leaves are alternate, 1 to 8 inches long, .5 to 3 mm wide, flat or folded, smooth to slightly rough-textured on the lower surface, minutely hairy on the upper surface.

The sheath is hairless except near the nodes. The ligule (membrane where the leaf joins the sheath) is less than 1 mm long and may be fringed with a few hairs. Nodes are smooth to minutely hairy. Stems are slender, erect to ascending, usually branched, thickened and bulbous at the base, minutely hairy below the nodes otherwise mostly hairless. Dense clumps are formed from a mix of vegetative and flowering shoots.

Fruit:

Mature florets drop off individually leaving the glumes behind on the stalk. Grains (seeds) are 1.5 to 2.4 mm long, amber-colored to brown.

Notes:

Muhlenbergia is a rather variable genus: clusters spike-like or an open panicle; glumes or lemmas awned, or neither; the callus (base of the floret) covered in long hairs or not; some with hairy stems or sheaths, others hairless; some branched, some not; clump forming or not; annual or perennial. What they have in common are spikelets usually single-flowered (occasionally with 2 or 3 florets), membranous ligules (occasionally also fringed with hairs), narrow leaves, glumes usually 1-veined, lemmas usually 3-veined, paleas 2-veined, and mature florets usually dropping off above the glumes (occasionally at the spikelet branch). There are about 70 species native to North America and more than 150 species worldwide.

In Minnesota, Plains Muhly is mostly found in counties west of the Mississippi River in dry, sandy or gravelly prairies, bluffs and rock outcrops. Of the 10 Muhlenbergia species known to be in Minnesota, it is one of two with very slender spike-like panicles and awnless spikelets. It is distingushed by the dense clumps, bulbous stem bases, glumes usually about ¾ as long as the spikelet, lemmas with sparse appressed hairs, ligules less than 1 mm long, and stems minutely hairy around the nodes. It commonly becomes infected with a smut fungus, developing a fruiting body that is dark colored, very fragile, and contains dark spores.

Most similar is Mat Muhly (Muhlenbergia richardsonis), which is also known to become infected with smut but is mat-forming, lacks the thickened stem base, has ligules more than 1 mm long, glumes less than half as long as the spikelet, hairless lemmas, and is found in moist to wet habitats. The spike-like panicle also resembles some Sporobolus species, which typically have some or all the panicle branches hidden inside the sheaths, and also lack the thickened base.