Flower:

Several to numerous clusters ¾ to 1+ inch long at the tip of the stem, each cluster oval to cylindric and loosely arranged with 10 to 20 spikelets (flower clusters), the spikelets arranged bottle-brush fashion on all sides of the cluster stalk, widely spreading to ascending. The 4 to 10 auxiliary clusters have stalks ¾ to 5 inches long, with 1 to 3+ clusters at the tip of a stalk. At the base of the group of clusters are 3 to 6 leaf-like bracts of varying lengths, V-shaped in cross-section, 2 to 12 inches long, all mostly ascending.

Spikelets are flattened, linear-oblong in outline, 15 to 20mm (½ to ¾ inch) long, with 6 to 34 florets, each subtended by a scale. Florets have 3 stamens and a 3-parted style. Scales are 1.8 to 2.7mm long, initially green turning straw-colored to golden or dark brown, lance to egg-shaped usually widest at the middle, with 3 to 5 ribs on each side and a green or brown midrib that is pointed at the tip. The scales are arranged on opposite sides of the central spikelet stalk (rachilla), overlapping and appressed to ascending. A narrow, papery wing runs along each side of the rachilla internode from the lower edge of the floral scale to the next scale below.

Leaves and stems:

Leaves are basal and alternate with 3 to 10 stem leaves near the base, bright yellowish-green, flat to V-shaped in cross-section, 2 to 6.5mm wide, 8 to 30 inches long, the longest leaves usually longer than the stem. Basal sheaths are brown to reddish-brown. Stems are single or multiple from the base, erect to ascending, fairly stout, 3-sided with sharp angles, and smooth. Plants may form loose clumps, form colonies from stolons and scaly rhizomes, and propagate vegetatively from small, hard tubers that develop at rhizome tips.

Fruit:

The floral scales and rachilla both persist at maturity. Achenes are 1.1 to 1.5mm long, brown when mature, 3-sided, generally elliptic in outline, slightly tapered to the base with a short stalk-like appendage (stipe), and more rounded at the tip. Achenes are often poorly developed and don't reach maturity.

Notes:

Cyperus esculentus is a common garden weed and agricultural pest with a gobal distribution, though in parts of the world it is cultivated for its edible tubers. It is very difficult to control once established, since it is resistant to most chemical treatments and mechanical or manual methods of control do not typically eliminate all the abundant tubers from which it regenerates. While the tubers and bright yellow-green foliage are distinctive characteristics, the bottle-brush like clusters are similar to other Cyperus species, notably Cyperus odoratus, Cyperus engelmannii, Cyperus strigosus and Cyperus erythrorhizos, none of which produce tubers. In addition, C. odoratus and C. engelmannii have spikelets that break apart between the florets, C. strigosus floral scales are much larger, 3 to 6mm long, and C. erythrorhizos has smaller scales, only 1 to 1.5mm long, that are typically more densely packed in slender cylindrical clusters and are darker reddish-brown.

While some references treat Cyperus esculentus as native to North America, it is not considered native in Minnesota. One recent study suggests it originated in Africa and migrated to the New World in pre-Columbian times via ocean currents, since the seeds, tubers, stolons and rhizomes can all float, and this method of long distance dispersal has been documented for other species. Here it morphed into new genotypes, adapted to cooler temperatures, and developed the invasive tendencies it is known to have today. There are currently 4 recognized varieties, distinguished by arrangement of spikelets, shape of floral scales, and size of anthers and styles: var. esculentus is considered the Old World species from which cultivated crops originated, vars heermannii and macrostachyus have limited ranges in the southern US into Central America, and var. leptostachyus, common across North America and considered invasive, described above.