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.
Phenology: Flowering spring.
Habitat: Muck of deep sphagnous seep bogs in longleaf pinelands
Elevation: 0–100 m
Discussion
Eriocaulon nigrobracteatum is a very limited, local endemic whose relationships with E. aquaticum should be clarified.
Of conservation concern.