Plants erect, emergent or floating, 30-120 cm. Stem terete, nearly always branched above. Leaves linear, 15-20 mm broad, triquetrous at the base. Branches bearing globose heads borne in the axils of large, leafy sheathing bracts, proximal end of branches bearing 1-3 female heads, male heads many at the distal end. Male flower with 3 or more connate or free stamens; anthers bibbed, basifixed, 1-1.5 nun long; filaments 3-5 mm long; perianth segments linear-spathulate, thickened, dark brown-black at apex, entire, 2-3 x 1-1.5 mm. Female flowers sessile; perianth segments 3 or more (usually 4), 1.5-3 x 1-1.5 mm, mostly spathulate, sometimes lanceolate-oblong, thickened, dark brown-black at apex, entire; ovary usually unicarpelate; style simple or bifurcate; stigmas 1 or 2, linear. Fruits obpyramidal below and domed-conical above, distinctly angled, usually sessile.