Hydrocharitaceae

Submersed or partially emergent, aquatic, non-woody (herbaceous), freshwater perennials, rooted or free-drifting. Plants with two very different structural patterns.

Each flower usually produces either pollen or seeds, on the same plant or separate plants; pollen-producing flowers usually separate individually and float to the surface. Individual seed-producing flowers or cymes of pollen-producing flowers supported by a spathe formed by 1-2 bracts; in seed-producing flowers, spathe forms a tube around ovary. Flowers usually radially symmetrical. Sepals and petals each 3, separate. Stamens 2-9. Carpels, 3-6, fused to form a single pistil with a compound ovary; ovary located below point of attachment of other flower parts (inferior); styles 3-6, each often split into two. Fruit a capsule.

Eelgrass with long ribbon-like basal leaves that have a row of air spaces on each side of the central vein. Pollen-producing flowers numerous. Seed-producing flowers solitary, reaching the surface on a very long spiral stalk. Capsule long and cylindrical, with many seeds, becoming submerged as its stalk recoils after fertilization.

Waterweed with leaves in whorls of 3 (or in pairs) along the stem. Flowers single, in leaf axils. Pollen-producing flowers with stamen stalks fused into a short column. Seed-producing flowers raised to the surface by a long slender stalk-like floral tube, or unstalked and breaking loose at maturity, floating to the surface where buds open and sepals spread. Capsule leathery, egg-shaped, with few seeds.