1 Inflorescence with > 30 flowers; fruit 1-seeded, indehiscent, a utricle; seeds smooth; leaves lanceolate to ovate, 1.5-10× as long as wide, the base cordate, truncate, or cuneate

1 Inflorescence with < 30 flowers; fruit 10-200-seeded, a capsule; seeds longitudinally winged; leaves either reniform or ovate, 0.5-1.5× as long as wide, the base cordate or rounded, or narrowly linear, 20-50× as long as wide, the base attenuate.

..2 Leaves membranous; petioles never expanded into air-filled floats; perianth lobes linear to oblanceolate, 0.4-2.0 cm long; stamens 3

..2 Leaves coriaceous; petioles either expanded into air-filled floats or not; perianth lobes ovate, 1.3-3.7 cm long; stamens 6.

....3 Herbs procumbent-emergent, stems elongate; sessile leaves late deciduous, rarely persistent in mature plants, petiolate leaves distichously-alternate, evenly distributed along the stem; perianth funnelform (the corolla limb expanding gradually from the widening corolla tube); style glabrous

....3 Herbs erect emergent or free-floating, stems inconspicuous; sessile leaves early deciduous, petiolate leaves spirally-alternate, congested at the apex of the stem; perianth salverform (the corolla limb spreading abruptly at a nearly right angle to the straight corolla tube); style glandular-pubescent.

......4 Erect emergents, never with inflated petioles; herbs never producing stolons; ligule truncate; inflorescences erect at post-anthesis, emerging from an inflated leaf-sheath, basal bract flat; flowers ca. 2-3 cm in diameter, perianth tightly enclosing the developing fruit; seeds subglobose to broadly oblong

......4 Free-floating aquatics, with inflated petioles; herbs stoloniferous; ligule flabellate, petioles generally inflated; inflorescences deflexed post-anthesis and in fruit, emerging from a non-inflated leaf-sheath, basal bract tubular; flowers ca. 4-6 cm in diameter, perianth loosely enclosing the developing fruit; seeds oblong