Perennials, 10-30 cm (aquatic). Stems ascending, unbranched or branched (rooting at proximal nodes). Leaves cauline; opposite; sessile; blades 1- or 3-nerved, broadly oblanceolate or 3-lobed, ultimate margins coarsely toothed, faces sometimes pilose and glabrescent or glabrous, gland-dotted. Heads discoid, borne singly. Involucres hemispheric or broader, 6-9 mm diam. Phyllaries persistent, 25-30 in 2-3+ series, not notably nerved, ovate to lanceolate or linear, ± equal (herbaceous to membranous). Receptacles convex to conic, epaleate (warty). Florets 75-100+; corollas white, throats broadly campanulate (notably wider than tubes, lengths ca. 1 times diams.); styles: bases not enlarged, glabrous, branches linear-filiform. Cypselae prismatic, 4-5-ribbed, sparsely gland-dotted and sparsely hairy (hairs forked); pappi 0. x = 15-