Flower:

1 to 10 clusters up to 1 inch long at the tip of the stem, each cluster with 3 to 18 spikelets (flower clusters). The main cluster of spikelets is stalkless and mostly inverted cone-shaped (obconic) in outline, auxiliary clusters are usually smaller, on stalks ½ to 5 inches long, obconic to oblong-elliptic in outline. At the base of the group of clusters are 3 to 8 leaf-like bracts of varying lengths, mostly flat, 1 to 8 inches long, all erect to slightly ascending.

Spikelets are flattened, oblong in outline, up to 2.5cm (~1 inch) long, with 3 to 14 florets, each subtended by a scale. Florets have 3 stamens and a 3-parted style. Scales are 2.5 to 3.5mm long, whitish to straw-colored and sometimes red-spotted, broadly lance-elliptic, 2 or 3-ribbed per side with a green midrib that extends to an awn .2 to 1mm long. The scales are arranged on opposite sides of the central spikelet stalk (rachilla), ascending and overlapping, sometimes barely so.

Leaves and stems:

Leaves are few, basal and alternate but near the base, flat or V-shaped in cross-section, 2 to 8mm wide, 6 to 14 inches long, and rough along the edges. Basal sheaths are brown to reddish-brown. Stems are single or few from the base, erect to ascending, slender, 3-sided with sharp angles, and rough at least on the upper stem. Plants form loose clumps from short, knotty rhizomes.

Fruit:

The floral scales and achenes (seeds) drop off individually when mature, leaving the naked stalk behind. Achenes are 2 to 3mm long, 1 to 1.5mm wide, dark brown to blackish when mature, 3-sided, broadly elliptic in outline, somewhat tapered at the base and more rounded at the tip end.

Notes:

Cyperus schweinitzii is a common flatsedge of dry, sandy soils. It is one of three Cyperus species in Minnesota that prefer dry rather than wet habitats, the other two are Cyperus lupulinus and Cyperus houghtonii, both of which are much less common and both of which have smooth stems with rounded angles, where C. schweinitzii has sharp angles and is rough at least on the upper stem. In addition, C. houghtonii has smaller scales (2.5mm long or less), the midrib tip only .1 to .2mm long. C. lupulinus typically has a single, smaller, hemispheric cluster densely packed with up to 60 spikelets, occasionally with 1 to 4 smaller, stalked spikelet clusters. C. schweinitzii hybridizes with C. lupulinus, the offspring, C. ×mesochorus, having intermediate characteristics in number of spikelet clusters, more widely ascending bracts than C. schweinitzii, and awns on the scales .4 to .5mm long.