Flower:

A panicle at the tip of the stem 3 to 20+ inches long, pyramidal in outline at flowering time with mostly ascending to spreading branches, sometimes nodding to one side, and the lowest branches often partially enclosed in the uppermost leaf sheath. Spikelets (flower clusters) are overlapping on the tip half or so of a branch. Spikelets are lance-elliptic in outline, somewhat compressed, 4 to 6 mm (to ¼ inch) long, light gray-green, with a single floret.

At the base of a spikelet is a pair of bracts (glumes), both awnless, keeled, rough-textured along the veins with hair-like teeth, pointed at the tip, thin with whitish edging, the lower glume 3.5 to 5 mm long and 1-veined, the upper glume to 6 mm long and 3-veined. Florets are surrounded by a pair of bracts (lemma and palea), the lemma 3-veined, as long as or slightly shorter than the upper glume, pointed at the tip, keeled with a straight awn .2 to 1.5 mm long that arises from just below the lemma tip; the palea is slightly shorter than the lemma and 1-veined. The floret is on a short stalk (rachilla) that extends about .1 mm above the base of the palea.

Leaves and stems:

Leaves are alternate, number 5 to 10 and evenly spaced along the stem, 6 to 12+ mm (to ½+ inch) wide, 6 to 13 inches long, hairless, smooth to rough on both surfaces and along the edges, flat, and commonly twisted near the base so the underside faces up.

The sheath is hairless. The ligule (membrane where the leaf joins the sheath) is 2 to 10 mm long, fragile and usually shredded, lacks a fringe of hairs and is slightly to strongly tinged brown. Nodes are smooth. Stems are unbranched, hairless, mostly erect, often thickened and bulbous at the base, single or a few from the base forming loose clumps.

Fruit:

Spikelets turn light brown at maturity, the entire spikelet dropping off leaving the naked stalks behind on the branch. Grains are 2.1 to 2.8 mm long.

Notes:

Sweet Woodreed is an occasional to common grass primarily found in moist to wet wooded habitats in the southern half of the state, occasionally in more open or mesic sites. Cinna grasses are distinguished by their single-flowered spikelets with only 1 stamen (most grasses have 3), spikelets dropping off below the glumes when mature; awnless glumes; hairless lemmas with a very short awn arising from just below the tip; paleas nearly as long as the lemmas. Cinna is considered a cool-season grass but does not flower until mid to late summer into fall.

Cinna arundinacea is further distinguished by spikelets 4 to 6 mm long; upper glume 3-veined; 5 to 10 stem leaves to 13 inches long, 6 to 12(19) mm (average ~½ inch) wide, commonly twisted near the base so the underside faces up; ligule up to 10 mm long, usually shredded and brownish; stem bases thickened and bulbous. The lowest panicle branches are often partially enclosed in the uppermost leaf sheath, and panicle branches may become nodding. It is most similar to the related Drooping Woodreed (Cinna latifolia), which is present primarily in the northern half of Minnesota, and is a more slender plant with fewer leaves (4 to 7) not usually twisted near the base, smaller spikelets (2.5 to 4 mm), the upper glume is 1-veined, ligules are usually whitish, and stem bases not bulbous.