Fimbristylis autumnalis is an annual sedge, tufted, to 20 cm tall, stems flattened, often rough-edged.
Leaves to 0.4 cm wide, shorter than inflorescence, ligule of short hairs; inflorescence bracts sheathless, mostly shorter than flowering stems.
Flower spikelets 0.3-0.7 cm long, brown, in loose, branched, umbrella-shaped clusters, scales keeled, bristle-tipped, achene 0.1 cm long 3-sided.
Wetland status: FACW.
Frequency in NYC: Very infrequent.
Habitat: Moist to wet soil, often in disturbed habitats, sandy soil.