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Annuals, usually submerged with only the heads emergent, c. 100(-260) mm tall. Leaves rosulate, linear-acuminate, with long filiform tips, thin, soft. Capitula small, depressed-globose, 3-5 mm in diam., shiny black; peduncles erect, thin; involucral bracts c. 6, ovate; floral bracts smaller, receptacle shortly cylindrical, glabrous or with a few long soft hairs. Female flower, sepals 3, c. 2.5 mm long, equal, half-folded, enclosing inside of flower, keel convex; petals 0, rarely 1, 2 or 3, small, linear; ovary 3-lobed; style with 3 stigmas. Male flower, few towards apex; sepals linear, fused below to form an oblique 3-lobed tube; petals 3, minute; stamens 6, black. Capsule 3-lobed; seeds with white transverse, fringed ridges.
Annual herb, up to 340 mm high; usually submerged, except for black heads. Leaves in basal rosettes; blade linear, usually < 50 mm long and < 2 mm wide. Flowers: heads small, shiny, jet-black; anthers black; petals usually absent; Feb., Mar. Seeds testa with transverse, white, fringed ridges.
Annual herb, up to 100 mm tall. Leaves in basal rosettes. Anthers black. Petals usually absent. Plant usually submerged, except for black capitula. Testa of seed with transverse, white, fringed ridges. Flowers black.
