Flower:

Loose, branching cluster at the top of the stem, 1 to 2½ inches long, with 1 or 2 branches per node. Branches are up to 1½ inches long, mostly ascending, sometimes spreading, with 2 to 5 spikelets (flower clusters) per branch. Spikelets are loosely overlapping at the tip of a branch, oblong-elliptic in outline, have a single floret, and a stalk more or less as long as the spikelet.

At the base of a spikelet is a pair of bracts (glumes), both about equal in size and shape, thin and papery, hairless, awnless, weakly 5-veined, oblong, blunt or straight across at the tip, 3.5 to 4 mm (to ~1/8 inch) long, and usually slightly shorter than the floret, sometimes slightly longer. Florets are surrounded by a pair of bracts (lemma and palea), the lemma leathery, brown at maturity, densely hairy with mostly appressed hairs, the body 3.5 to 4.5 mm long tapering to a straight or bent awn 1 to 2 mm long that falls off before maturity; the palea is similar to the lemma but lacks the awn.

Leaves and stems:

Leaves are mostly basal, 4 to 10 inches long, .5 to 1.8 mm wide, flat or rolled up along the edges (involute), rough-textured, and stiff. Stem leaves are few, up to about 4 inches long, and mostly near the base.

The sheath is rough-textured with thin, papery edging. The ligule (membrane where the leaf joins the sheath) is .5 to 2.5 mm long, pointed or straight across at the tip and lacks a fringe of hairs. Nodes are smooth. Stems are unbranched, hairless, mostly erect, multiple from the base and forming loose to dense clumps.

Fruit:

The glumes become widely spreading as each grain matures, the florets dropping off individually leaving the glumes behind on the stalk. Grains (seeds) are about 1.8 mm long, narrowly lance-elliptic.

Notes:

Mountain Rice Grass, also known as Piptatheropsis pungens (formerly Oryzopsis pungens), is a fairly common forest species in Minnesota, found in dry, rocky or sandy soils, often in Jack pine stands. It is distinguished from other grasses by the loose cluster of single-flowered spikelets usually 4 mm long (excluding awns) or less, thin, hairless glumes as long as the spikelet that become spreading at maturity, lemmas with short awn (2mm or less) that drop off before maturity, lemma surface covered in mostly appressed hairs, leaves less than 2mm wide that are flat or involute, and hairless ligules up to 2.5mm long. The overall form may be similar to Black-fruited Rice Grass (Patis racemosa, formerly Piptatherum racemosum or Oryzopsis racemosa), Rough-leaved Rice Grass (Oryzopsis asperifolia), and Canadian Rice Grass (Piptatherum canadense or Piptatheropsis canadensis, formerly Oryzopsis canadensis), all of which have persistent, long awns.