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Herb 12–70 cm long, submerged aquatic in water to c. 1 m deep. Leaves crowded, cauline, filiform, 2.5–16 cm long, 1-nerved. Peduncle 5–27 cm long. Sheath 25–50 mm long. Flower heads depressed-globular, 2.5–5 mm long, 3.5–6 mm wide. Involucral bracts black, oblong to broadly obovate, 0.95–1.75 mm long, 0.5–1.3 mm wide, obtuse, glabrous, strongly reflexed at maturity. Floral bracts black or straw-yellow with black apex, obovate, 0.9– 1.8 mm long, 0.43–0.7 mm wide, acute to obtuse, pubescent with easily deciduous white hairs at apex or rarely glabrous. Receptacle glabrous or rarely sparsely hairy, conical. Male flowers 0.9–1.5 mm long; sepals 3, fused but split on one side to form a spathe which is 3-lobed and readily splitting with age, black to hyaline, 0.8–1.5 mm long, 0.2–0.53 mm wide, obtuse to truncate, pubescent with apical fringe of white hairs or rarely glabrous; petals 3, hyaline, equal, acute, pubescent with apical fringe of white hairs or rarely glabrous; stamens 6; anthers black. Female flowers: sepals 3, dark grey to black or rarely hyaline, equal, elliptic and shallowly navicular, lacking dorsal keel or wing, 0.7–1.7 mm long, 0.35–0.53 mm wide, obtuse or truncate, pubescent with apical fringe of white hairs or rarely glabrous; petals 3, dark grey to black or hyaline, equal, linear to elliptic, 0.6–1.5 mm long, 0.1–0.3 mm wide, acute or obtuse to truncate, pubescent with apical fringe of white hairs or rarely glabrous; ovary 3-locular. Seeds 0.45–0.6 mm long, 0.32–0.43 mm wide; epidermal cell outline faint and with obscure peg-like projections on transverse walls.
Plants mostly submerged. Stems ca. 25 cm. Leaves filiform, 3--4 cm × ca. 0.2 mm, 1-veined. Scapes 5--15, to 11 cm, 6-ribbed; sheath 2--2.5 cm; receptacle subglabrous or villous; heads dusky, subglobose, ca. 2.5 × 3 mm; involucral bracts reflexed, straw-colored, ovate, ca. 1 mm, membranous, glabrous; floral bracts orbicular to oblanceolate, abaxially white clavate hairy toward apex or glabrous. Male flowers: sepals spathelike, abaxially shortly hairy toward (2 or)3-lobed apex, lobes truncate at apex; petals 3, elliptic to subulate, small, anterior one slightly larger than others, adaxially white clavate hairy, abaxially white clavate hairy toward apex, gland black, sometimes absent; anthers black. Female flowers: sepals 3, free, boatlike to obovate, abaxially white clavate hairy toward margin; petals 3, free, oblanceolate-linear, unequal, membranous, gland black, sometimes absent; ovary 3-loculed; style 3-cleft. Seeds narrowly ovoid, 0.3--0.4 mm; testa hexagonally reticulate, prickles 1 or 2 per cell, linear, slimy coated. Fl. and fr. Aug--Oct.
Capitula blackish, small, seldom exceeding 4 mm. diam.
Stems elongate, clothed with numerous filiform leaves
Scapes generally numerous
Floating aquatic
