Cyperus diandrus is an annual C4 sedge (Li et al. 1999), tufted, 10-20 cm tall, stems slender.
Leaves often as long as flowering stem; inflorescence bracts 3, the lowest to 15 cm long, stalks of spikes (rays) 1-3, to 6 cm long.
Flower spikelets reddish-brown to greenish, 6-10 per spike, 0.8-1 cm long, 0.2-0.3 cm wide, very flat, scales egg-shaped, about 0.3 cm long, becoming red-purple at tip and along margins, colorless along midrib,
Fruit: achenes lens-shaped 0.1 cm, style persistent; blooms and fruits June-Oct.
Wetland status: FACW.
Frequency in NYC: Very infrequent.
Habitat: Wet soil, shores.