Cyperus filiculmis Vahl var. macilentus Fernald, Rhodora 8: 128. 1906; C. macilentus (Fernald) E. P. Bicknell

Culms (3–)10–30(–40) cm × 0.4–0.8 mm. Leaves 5–20 cm × 0.8–2.7 mm. Inflorescences: spikes densely ovoid, 8–16 mm; rays 0 or 1–3, 1–4 cm; bracts 2–4, 4–15 cm. Spikelets 20–60, 3–7 × 2.5–3.5 mm; floral scales 3–7, 1.8–2.5 × 1.4–1.8 mm, margins clasping achene, apex mucronate, mucro 0.05–0.2 mm. Achenes 1.4–1.8 × 0.6–0.9 mm.

Fruiting summer. Various well-drained, open places; 0–1000 m; N.B., N.S., Ont., Que.; Conn., Del., D.C., Ga., Ill., Ind., Iowa, Maine, Md., Mass., Mich., Minn., Nebr., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., Vt., Va., W.Va., Wis.