Cyperus retrorsus is a perennial C4 sedge (Li et al. 1999), to 1 m tall from a short, tuberous rhizome, stems smooth, very slender.
Leaves shorter than flowering stems, to 0.5 cm wide.
Flower spikelets numerous, crowded, radiating horizontally, to 0.6 cm long, with 1-3 flowers, scales thin, egg-shaped 0.2 cm; inflorescence bracts 4-8, mostly longer than inflorescence, spike stalks (rays) 5-9, to 10 cm long, spikes dense, short-cylindrical, to 2.5 x 1.2 cm.
Fruit an achene, 3-sided, oblong to 0.15 cm; blooms and fruits July-Oct.
Wetland status: FAC-.
Frequency in NYC: Rare (NYS S1, E).
Habitat: Sandy barrens, coastal sands.