1. Sepals and petals 5; capsules elongate, with conspicuous pedicels.

L. peploides

1. Sepals and petals (if present) 4; capsules short, sessile or on pedicels up to 5 mm long.

2. Leaves opposite; plants prostrate or floating in shallow water, usually rooting at the nodes.

L. palustris

2. Leaves alternate; plants erect.

3. Flowers on distinct pedicels ca. 2-5 mm long; petals conspicuous, about equaling the sepals; roots usually tuberous-thickened.

L. alternifolia

3. Flowers sessile or nearly so; petals apparently none; roots not becoming thickened (but plant stoloniferous and the stem often with well developed spongy tissue at base).

4. Bractlets at or (usually) above base of ovary 2.5-6 (-8) mm long; capsules, leaves, and stem glabrous.

L. polycarpa

4. Bractlets at base of ovary 0-2.6 mm long; capsules, leaves, and upper part of stem at least sparsely strigose.

L. sphaerocarpa