Eleocharis tuberculosa is an annual spikerush, tufted, stems flattened, 20-80 cm tall.
Leaves bladeless, sheaths only.
Flower spike egg-shaped, 0.5-1.5 cm long, tip pointed, scales rounded above, straw-color to dull brown, clasping achene.
Fruit a dry achene 3-sided, about 0.1 cm, widest above middle, with many rows of tiny warts, tubercle narrow-based, then widened, about as large as achene, sitting on top like an outsized hat, June-Sept.
Wetland status: OBL.
Frequency in NYC: Rare (NYS S2, T).
Habitat: Wet, often sandy soil, swamps, shores.