Phaeocephalum perplexum (Britton) House

Plants perennial, cespitose, 50–110 cm; rhizomes absent. Culms lax, often excurved, slender, ± te-rete or trigonous. Leaves ascending, exceeded by culm; blades linear, proximally flat, 1.5–2.5 mm wide, apex trigonous, subulate, tapering. Inflorescences: clusters 3–4, widely spaced, narrowly, compactly, or diffusely turbinate; leafy bracts exceeding proximal clusters. Spikelets deep red brown, ovoid to broadly ellipsoid, 2–3 mm, apex acute to acuminate; fertile scales broadly elliptic to obovate or orbiculate, 1.4–2(–2.5) mm, apex rounded to notched, midrib short excurrent. Flowers: perianth bristles 0–3, vestigial when present. Fruits 2–4 per spikelet, 1.5 mm; body pale brown to brown, strongly flattened, orbicular to broadly obovoid, 1–1.3 × 0.9–1.2 mm, surfaces sharply transversely wavy rugose, intervals finely vertically striate with rows of linear rectangular alveolae; tubercle depressed, triangular, flattened, 0.2–0.3 mm, base lunate.

Fruiting late spring–fall or all year (south). Sands and peats of pond and lakeshores, depressions in savannas and flatwoods, or seeps; 0–400 m; Ala., Fla., Ga., La., Miss., N.C., S.C., Tenn., Tex., Va.; West Indies (Cuba, Dominican Republic); Central America.

In habit and in shape, size, and color of spikelet, Rhynchospora perplexa strongly resembles R. microcarpa, a species with which it is commonly associated in the Coastal Plain. An examination of the fruit shows those of R. perplexa to be flattened, with fewer and much coarser transverse ridges, the intervals with very narrow vertical alveolae. The perianth in most instances is absent or rudimentary. Fruit of R. microcarpa is biconvex with more transverse ridges (eight or more), the intervals more coarsely alveolate; its perianth bristles are six, evident, extending at least halfway up the fruit body.