Plants perennial, densely cespitose, 20-50 cm; rhizomes absent. Culms erect to excurved, lax, filiform, leafy, ± terete. Leaves exceeded by culm, ascending; blades filiform, ± terete, margins strongly involute, apex trigonous, sulcate, tapering. Inflorescences: spikelet clusters mostly 2-3, sparse to dense, oblong to broadly or narrowly turbinate; leafy bracts setaceous, exceeding clusters. Spikelets pale red brown, lanceoloid, 3-3.5 mm, apex acute; fertile scales mostly elliptic, 2-2.5 mm, apex acute, sometimes apiculate. Flowers: bristles mere nubs or 1-2, to 0.3 mm. Fruits mostly 2 per spikelet, 1.5-1.6 mm; body red brown with pale center, lenticular, broadly obovoid to orbicular, margins pale, narrow, flowing to tubercle; surfaces smoothish, or faintly cancellate; tubercle flattened, triangular subulate, 0.3-0.5 mm.

Fruiting late spring-fall. Moist sandy peaty substrates in savannas or savanna bog transition, ditches, and moist, disturbed areas; Ala., Fla., Miss.; West Indies; Central America.

Rhynchospora brachychaeta is quite possibly adventive; most of its localities in the flora are in disturbed areas near the coast. It is similar to the widespread native R. chapmanii, from which it is distinguished by its more numerous spikelet clusters, the darker spikelets, the achene faces brown with pale centers (rather than pale with brown ends), and the relatively more developed perianth.