Herbs, perennial, 5--15(--19) cm. Leaves linear-attenuate, 0.5--1.5(--4) cm, apex subulate. Inflorescences: scape sheaths longer than principal leaves; scapes filiform, 0.3--0.4 mm, 4-ribbed; mature heads blackish at level of involucre, white above it, hemispheric to globose, 3--4(--5) mm wide, soft; receptacle glabrous; involucral bracts spreading, not obscured by bracteoles and flowers, blackish, very lustrous, broadly ovate to orbiculate, 1--3 mm, margins entire to erose, apex broadly rounded, glabrous; inner bracts, receptacular bracteoles blackish or with pale base, broadly to narrowly ovate, 2--3 mm, margins somewhat erose with age, apex rounded or apiculate, margins and abaxial surfaces with white, club-shaped hairs, apically ciliate. Staminate flowers: sepals 2, gray-brown, broadly spatulate to oblong-obovate, curved, keeled, 1--1.2 mm, keel and margin with white, club-shaped hairs; androphore club-shaped to campanulate, flaring; petals 2, oblong-obovate, nearly equal, 1 mm, apex ciliate and abaxially with white, club-shaped hairs; stamens 4; anthers black. Pistillate flowers: sepals 2, gray, oblong, curved, keeled, 1 mm, adaxial surfaces pilose, hairs translucent, sharp, apically with white, club-shaped hairs; petals 2, pale, short-stipitate or nearly sessile, oblong, 1 mm (narrower and longer than those of E. koernickianum), apex obtuse, adaxial surface and margins with white, club-shaped hairs; pistil 2-carpellate. Seeds brown, nearly round, 0.3 mm, obscurely reticulate, alveolae irregularly and horizontally rectangular. Flowering spring. Muck of deep sphagnous seep bogs in longleaf pinelands; of conservation concern; 0--100 m; Fla. Eriocaulon nigrobracteatum is a very limited, local endemic whose relationships with E. aquaticum should be clarified.