Flower:

Usually a single, stalkless, hemispheric to round cluster up to 2/3 inch across (occasionally to 1¼ inch) at the tip of the stem, rarely with 1 to 4 auxiliary clusters on stalks up to 2½ inches long. A cluster has 15 to 60 spikelets (flower clusters). At the base of the group of clusters are 2 to 5 leaf-like bracts of varying lengths, mostly flat, 1 to 10 inches long, all widely spreading to bent downward (deflexed).

Spikelets are flattened, lance-oblong in outline, usually 3 to 7mm (1/8 to ¼ inch) long with 3 to 7 florets, occasionally up to 22mm (.9 inch) with up to 22 florets. Each floret is subtended by a scale, has 3 stamens and a 3-parted style. Scales are usually 1.8 to 2.5mm long (occasionally to 4mm), green to whitish to light reddish-brown, broadly lance-elliptic, 3 to 5-ribbed per side with a green midrib that extends to a minute awn up to .2mm long. The scales are arranged on opposite sides of the central spikelet stalk (rachilla), erect to ascending and overlapping, sometimes barely so.

Leaves and stems:

Leaves are few, basal and alternate but near the base, flat to V-shaped in cross-section, 1 to 3.5mm wide, 2 to 16 inches long, rough along the edges and usually shorter than the stem. 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 to dense clumps and may make small colonies from short, knotty rhizomes.

Fruit:

The floral scales and achenes (seeds) drop off individually when mature, leaving the naked stalk behind, the scale edges usually tightly wrapping the achene, sometimes loose (depending on the subspecies). Achenes are 1.7 to 2.2mm long, .8 to 1.2mm wide, dark brown to blackish when mature, 3-sided, oblong-elliptic in outline, somewhat tapered to the base and more rounded at the tip end.

Notes:

Cyperus lupulinus, in some older references known as Cyperus filiculmis, is an occasional 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 schweinitzii and Cyperus houghtonii, both of which typically have multiple spikelet clusters each with 18 or fewer spikelets and erect to slightly ascending bracts, where C. lupulinus usually has a single hemispheric cluster with 15 to 60 spikelets and widely spreading to deflexed bracts. There are 2 recognized subspecies, both of which are present in Minnesota: subsp. lupulinus, uncommon in the state, with 5 to 22 scales per spikelet and floral scales 2.5 to 4mm long with edges that are loose around the achene, and subsp. macilentus, much more common, with clusters only up to 16mm (2/3 inch) across, 3 to 7 scales per spikelet and scales 1.8 to 2.5mm long that tightly wrap the achene. All of our images are subsp. macilentus. C. schweinitzii hybridizes with C. lupulinus, the offspring, C. ×mesochorus, having intermediate characteristics in number of spikelet clusters, strongly ascending bracts, and awns on the scales .4 to .5mm long.