Flower:

Dense spike-like branching cluster at the top of the stem, 2 to 6 inches long, the short branches ascending to erect at flowering becoming more appressed in fruit. Spikelets are short-stalked, green to purple-tinged, 4 to 7.5 mm (to ~1/3 inch) long, slightly flattened, lance-elliptic in outline and have usually 2 florets, occasionally 3.

At the base of a spikelet is a pair of bracts (glumes), both lance-elliptic with a pointed tip, keeled, usually smooth except along the keel, sometimes rough or sparsely hairy, the upper glume 4 to 7 mm long and 3-veined, the lower glume ¾ to nearly as long as the upper glume and 1-veined. Florets are surrounded by a pair of bracts (lemma and palea), the lemma 5-veined, hairless to minutely hairy, 4 to 5.5 mm long, notched and forming 2 pointed teeth at the tip with an awn arising from the upper third of the back, the awn 2.5 to 6.5 mm long and initially straight but becoming bent once or twice and spirally twisted below the bend; the palea is thin and papery, shorter and narrower than the lemma, somewhat rough along the keel. The thickened base of the floret (callus) and the stalk between florets (rachilla) are both hairy, the hairs up to 1 mm long.

Leaves and stems:

Leaves are basal and alternate, mostly erect, 1¼ to 4 inches long, 1 to 3.5 mm (to 1/8 inch) wide, lance-linear, flat or rolled in along the edges (involute), hairless to variously hairy.

Sheaths are hairless to variously hairy. The ligule (membrane where the leaf joins the sheath) is thin, .5 to 4mm long, rounded to straight across at the tip and not fringed with hairs. Nodes are smooth to variously hairy. Stems are erect, hairy on the upper stem, usually hairless below, multiple from the base forming clumps of mixed flowering and vegetative shoots.

Fruit:

Spikelets are light brown at maturity, the florets shedding individually as each grain matures, leaving the glumes behind on the stalk. Grains (seeds) are 1.5 to 3 mm long and hairless.

Notes:

Spike Trisetum is one of the most common flowering plants in the world, present on all continents except Africa. Throughout its range it is found in alpine meadows, tundra slopes, and shores. In Minnesota it is only found along the north shore of Lake Superior, in rock crevices and ledges and around rock pools. According to the DNR, it has only been found in about 35 locations and was thought to be protected by the remoteness and inaccessibility of the rocky shore, but the area has seen a boom of development and recreational use in the last 20 years, putting these fragile microhabitats at risk. It was listed as a Special Concern species in 2013 and is currently Threatened in Wisconsin.

Spike Trisetum is quite variable in degree of hairiness and some references note multiple varieties, but these are not recognized in Minnesota. It may be distinguished from other grasses by its rock habitat, hairless ligule, dense green to purple-tinged spike-like cluster, spikelets with usually 2 florets, lemmas 4 to 5.5 mm long with 2 teeth at the tip, a bent and twisted awn arising from upper third of the lemma, and hairy callus and rachilla. Somewhat similar is Poverty Grass (Danthonia spicata), a much more common species found in the same habitats that has spikelets with 4 or more florets, glumes distinctly longer than the spikelet, hairy lemmas, ligules a fringe of long white hairs, and curly persistent old leaves around the base. Also similar is the related Spike Oat (Avenula hookeri), a dry prairie species of the Great Plains, found only in northwest MN, has 3 to 6 florets in a spikelet, lemmas about twice the size (up to 13 mm long), and distinctive white edging on the leaves.