Flower:

Several to numerous clusters 3/8 to 1 inch long at the tip of the stem, each cluster densely packed with 40 to 80 spikelets (flower clusters), the spikelets arranged bottle-brush fashion on all sides of the cluster stalk, widely spreading with those at the tip erect to ascending. The 2 to 12 auxiliary clusters have stalks ¾ to 3 inches long, and are usually compound with 3 or more clusters at the tip of a stalk. At the base of the group of clusters are 5 to 8 leaf-like bracts of varying lengths, M-shaped in cross-section, 2 to 10 inches long, all spreading to ascending.

Spikelets are slightly flattened, 4-sided in cross-section, linear-oblong in outline, 3 to 8mm (1/8 to 1/3 inch) long, with 6 to 16 florets, sometimes more, each subtended by a scale. Florets have 3 stamens and a 3-parted style. Scales are 1.3 to 1.5mm long, reddish-brown to dark brown, lance to egg-shaped, with a green to brown midrib that is blunt or minutely pointed at the tip. The scales are arranged on opposite sides of the central spikelet stalk (rachilla), overlapping and appressed to ascending. The rachilla is minutely winged.

Leaves and stems:

Leaves are basal and alternate with 1 to 4 stem leaves near the base, flat to M-shaped in cross-section, 4 to 12mm wide, 2 to 12 inches long, about as long as or shorter than the stem. Basal sheaths are purplish. Stems are multiple from the base, erect to ascending, 3-sided often with rounded angles, and smooth. Plants form loose to dense clumps and have red, fibrous roots.

Fruit:

When mature, the floral scales drop off individually leaving the rachilla wings persisting like tiny scales on the stalk, and the lateral spikelets eventually breaking off from the base. Achenes are .5 to 1mm long, shiny light gray-brown to brown when mature, 3-sided, generally oval in outline, somewhat tapered at the base and more rounded at the tip.

Notes:

While the red roots of Cyperus erythrorhizos are distinctive, the bottle-brush like clusters are similar to other Cyperus species, notably Cyperus odoratus, Cyperus engelmannii, Cyperus esculentus and Cyperus strigosus, all of which have larger scales (more than 1.5mm long) and longer spikelets that are usually more loosely arranged than C. erythrorhizos. In addition, C. odoratus and C. engelmannii, both of which may be found growing with C. erythrorhizos, have spikelets that do not break off as a unit, but break apart between the florets. C. esculentus is leafier than C. erythrorhizos and produces tubers on its roots. C. strigosus has much larger scales, 3 to 4+mm long, that are typically more yellowish than reddish-brown.