Flower:

Spike-like panicle up to 6 inches long at the tips of branching stems, the panicle branches mostly erect, up to 1 inch long, typically crowded at the stem tip but the lowest branches somewhat separated. Short-stalked spikelets (flower clusters) are crowded and overlapping on each branch, each spikelet 3 to 8 mm (to ~1/3 inch) long, with a single floret.

At the base of a spikelet is a pair of bracts (glumes), both about equal in size and shape, 1-veined, hairless, awned at the tip, 3 to 8 mm long including the awn and 1.3 to 2 times as long as the floret. Florets are surrounded by a pair of bracts (lemma and palea), the lemma 2.2 to 4 mm long, narrowly lance-elliptic, 3-veined, sparsely long-hairy near the base, tapering to a pointed tip, occasionally with an awn up to 1 mm long; the palea is 2-veined, more or less as long as the lemma, and sparsely long-hairy near the base. The thickened base of the floret (callus) is covered in straight, white hairs up to about 1 mm long.

Leaves and stems:

Leaves are alternate, 1 to 6½ inches long, 2 to 5 mm wide, mostly flat, smooth to rough-textured, hairless. Sheaths are slightly rough and hairless. The ligule (membrane where the leaf joins the sheath) is up to 1.5 mm long, straight to jagged across the top and may have a sparse fringe of hairs. Nodes are smooth and typically shiny. Stems are erect, branched from about mid-stem, hairless, compressed and elliptic in cross-section. Branches can be rather leafy. Plants are not clump-forming, but create loose colonies from long, scaly rhizomes.

Fruit:

Mature florets drop off individually leaving the glumes behind on the stalk. Grains (seeds) are spindle-shaped, 1.4 to 2.3 mm long, 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.

Marsh Muhly has been found in a variety of habitats from dry prairies and rock outcrops to wet meadows and river banks, but most often in sunny sites. Of the 10 Muhlenbergia species known to be in Minnesota, it is distinguished by the loose colony-forming growth, stems usually branched from about mid-stem, nodes and the stem below the node hairless, awned glumes about equal in size that are up to twice as long as the floret, and the terminal, spike-like panicle. Florets are long-hairy on the callus and both lemma and palea are sparsely long-hairy near the base. The stem is elliptic in cross-section and may even be nearly flat near the panicle, easily felt when rolled between your fingers.

Marsh Muhly is most similar to Spike Muhly (Muhlenbergia glomerata), which has similar spikelets, but is unbranched or few-branched near the base, visibly hairy on nodes and stems just below the nodes, stems are round in cross-section, and the lowest panicle branches tend to be more widely separated.