Plants perennial, densely cespitose, 30–60(–90) cm; rhizomes forking, compact. Culms lax, leafy toward base, filiform, ± terete. Leaves ascending, exceeded by culm; blades filiform, to 0.5 mm, margins mostly involute, apex trigonous, tapering. Inflorescences mostly lax cymes or clusters of cymes, 1–2, sparse, turbinate, branches capillary; leafy bracts setaceous, exceeding proximal cymes, shorter than, equaling or slightly exceeding distal cymes. Spikelets red brown, fusiform lanceoloid, 5 mm, apex acute; fertile scales lanceolate, 3.5–4.5 mm, apex acute or acuminate, midrib included or short excurrent. Flowers: perianth bristles 6, exceeding tubercle base, antrorsely barbellate, basally setose. Fruits 1 per spikelet, 2.8–3 mm; body pale brown, obovoid pyriform, tumidly lenticular, 1.5–1 × 1 mm; surfaces transversely wavy rugose, intervals vertically striate with narrow, raised alveolae; tubercle flat, narrowly triangular-subulate, (0.8–)1–1.5 mm.

Fruiting spring–summer. Sands and peats of bogs, seeps, pond shores, flatwoods, and savannas; 0–200 m; Ala., Fla., Ga., La., Miss., N.C., S.C., Tex.

Rhynchospora stenophylla may occasionally be confused with the closely related R. rariflora but can be distinguished by its taller and wispier habit, its longer spikelets of narrower outline, and the distinctly longer fruit tubercle. Both species are usually found on wet substrates; R. stenophylla typically is found in the deepest bogs and sphagnous seeps.