Spikes:

Open, nodding, branching cluster at the top of the stem with numerous spikelets (flower clusters) grouped 3 to 7(15) at the end of short stalks, occasionally paired. Spikelets are 3.5 to 8 mm long (to ~1/3 inch), oval to egg-shaped, blunt at the tip, dull grayish-brown when young, turning more rusty brown with age. Florets are spirally arranged and are perfect (both male and female parts), each with a 3-parted style and subtended by a single scale.

At the base of the cluster, surrounding each of the lowest 3 to 6 main branches, are leaf-like bracts with reddish-brown to blackish sheaths. Bract blades are shorter than to much longer than the cluster, the shorter bracts erect to ascending and the longer bracts arching to reflexed (bent downward). Bracts at the base of auxiliary branches are scale-like and brown.

Leaves and stems:

5 to 10 leaves are alternately arranged along the stem, 8 to 32 inches long and 3 to 10 mm wide. Lower leaf sheaths are green to reddish-brown. Stems are mostly erect, round in cross-section and smooth. Plants form dense clumps from short rhizomes and a mix of flowering and vegetative shoots. Old leaves persist forming tussocks.

Fruit:

Fruit develops in mid to late summer, the mature achenes (seeds) dropping off individually and the scales dropping soon after. Scales are 1.1 to 2.2 mm long, oblong-elliptic to egg-shaped, blunt at the tip sometimes with a minute point, reddish-brown to blackish with a green or pale midrib that becomes rather inconspicuous. Achenes are .6 to .9 mm long, to .5 mm wide, oval-elliptic in outline, 3-sided, straw-colored to whitish at maturity. Surrounding the base are 6 whitish to light brown bristles that are several times longer than the achene and much contorted. The bristles extend out beyond the scale and give the cluster a woolly appearance.

Notes:

Scirpus cyperinus is a common wetland species found along lake and pond margins and in wet ditches. It closely resembles 3 other Minnesota Scirpus species: Scirpus atrocinctus, Scirpus pedicellatus, and Scirpus pendulus. All share the common traits of a leafy round stem, leaf-like bracts, a terminal cluster with nodding branches and numerous small spikelets, and achenes with contorted bristles much longer than the achene. Scirpus cyperinus, the most common of the 4, is most easily distinguished by the spikelets clustered in groups of (usually) 3 to 7 or more. The other 3 species have spikelets all or mostly single, occasionally paired.

S. cyperinus hybridizes with both S. atrocinctus and S. pedicellatus and fertile intermediates may be found when both parents are present, the hybrids cross-breeding with themselves and their parents, known as a hybrid swarm. As if they weren't challenging enough already...

Compare these with other Bulrush species, which may differ by their 3-sided stems, erect bracts that appear to be a continuation of the stem, essentially leafless stems, globular clusters of numerous small spikelets, bristles as long as or shorter than the achene, or other traits not as above.