Flower:

2 to 7 clusters up to ¾ inch long at the tip of the stem, each cluster with 5 to 12 spikelets (flower clusters). The main cluster of spikelets is stalkless and hemispheric in outline, auxiliary clusters are on stalks ½ to about 3 inches long, with spikelets arranged widely spreading to ascending and the terminal spikelet usually erect. At the base of the group of clusters are 2 to 4 ascending to spreading leaf-like bracts, the largest up to about 6 inches long and nearly erect.

Spikelets are flattened, linear-oblong in outline, up to 15mm (½ inch) long, with 8 to 30 florets, each subtended by a scale. Florets have 2 or 3 stamens and a 2-parted style. Scales are 2.5 to 3mm long, lance-oval, blunt at the tip, greenish-white with reddish-brown to maroon along the edge often just at the tip end, with a green midrib. The scales are arranged ascending and tightly packed, overlapping on opposite sides of the central spikelet stalk (rachilla).

Leaves and stems:

Leaves are basal and alternate, typically 1 to 3 per stem near the base, flat, 1 to 3mm wide, as long as or shorter than the flowering stem. Basal sheaths are brown to reddish-brown. Stems are multiple from the base, erect to prostrate, 3-sided and smooth. Plants form loose to dense clumps and often form dense colonies.

Fruit:

The floral scales and achenes (seeds) drop off individually when mature, leaving the naked stalk behind. Achenes are 1 to 1.2mm long, brown, lens-shaped and generally oval-elliptic in outline.

Notes:

Cyperus diandrus is found along lake and pond shores, wet meadows, and other low, seasonally wet areas. It is easily confused with the more common Cyperus bipartitus, which has clusters usually with 5 or fewer spikelets, floral scales that are maroon to reddish-brown except maybe along the edge, especially at the tip end, and the style is not persistent (see comparison photo below).