Flower:

Raceme-like branching cluster 2½ to 5 inches long at the top of the stem, the 2 to 9 branches each 1½ to 2¾ inches long, on very short stalks. Branches are all arranged on one side of the stem and erect to spreading, but mostly ascending. The central branch stalk (rachis) is densely hairy with 11 to 24 spikelets (flower clusters) all arranged on the underside of the rachis, packed in 2 rows. Spikelets are 4 to 5 mm (less than ¼ inch) long, 2 to 2.5 mm wide, oval-elliptic, slightly flattened, and have one fertile and one sterile floret though appear to be single-flowered. Spikelets are green to purplish brown. The spikelet stalk is densely covered in long, white hairs and has a yellowish cup-shaped structure at the tip.

At the base of a spikelet is a pair of bracts (glumes), the lower glume obscure and scale-like or absent altogether, the upper glume oval-elliptic, thin and papery, 3.4 to 5 mm long and as long as the spikelet, 5-veined, lacking a keel, and covered in fine, soft hairs. Florets are surrounded by a pair of bracts (lemma and palea), the sterile lemma much like the upper glume and appearing to be the second glume; the sterile palea is absent. The fertile lemma and palea are both thicker than the glume, oval-elliptic with a minute point at the tip (mucronate), about as long as or slightly shorter than the upper glume, awnless, veinless, hairless; the lemma edges curl around the floret and the palea edges.

Leaves and stems:

Leaves are alternate, erect to ascending, 4 to 8 inches long, about ¼ to ½ inch (5 to 13mm) wide, lance-linear with a long taper to a pointed tip, flat, minutely hairy on both surfaces, rough textured along the edges and typically minutely crinkled along one edge, especially near the base.

Sheath are hairless to variably hairy, often hairy along one edge. The ligule (membrane where the leaf joins the sheath) is a fringe of white hairs up to 1.3 mm long. Stems are leafy, hairless except in the flower clusters, multiple from the base forming loose clumps, erect or more often prostrate from the base but rising at a lower node (geniculate), and may root at the nodes forming colonies.

Fruit:

Spikelets are green to purplish at maturity, the entire spikelet dropping off leaving the hairy stalk behind. Grains (seeds) are oval-elliptic, 3 to 4 mm long.

Notes:

Hairy Cupgrass was unintentionally introduced from Asia as a seed contaminant and has been considered primarily an agricultural weed of the midwest. It made its way to Minnesota in the late 1960s, first recorded in a corn field in Blue Earth County. While the official records indicate it is not very widespread in the state, it is very much an under-reported species and we've been told by a DNR ecologist that it is becoming a significant pest plant in certain high quality habitats, describing it as the “Reed Canary Grass of rock outcrops”. Though it is an annual and does not produce the dense mat of perennial rhizomes RCG does, it can root at the nodes and create a similarly dense stand. In a sensitive areas like rock outcrops where topsoil is thin and sparse, it can consume large swaths of the available soil and crowd out native plants. Hairy Cupgrass is not likely to be confused with other grasses: the hairy leaves, ligules and nodes, raceme-like cluster with 3 to 9 branches all on one side of the stem, hairy rachis with 2 rows of single-flowered, oval-elliptic, awnless spikelets 4 to 5mm long, finely hairy glumes, spikelet stalks covered long, white hairs, and the mature spikelets dropping of in their entirety are a pretty unique combination.