Zosteraceae

Smooth, slender, grass-like, aquatic, marine, non-woody (herbaceous) perennials, growing completely under water at high tide; from a creeping rhizome. Stems jointed, branching and leafy.

Leaves alternate, ribbon-like, often in 2 vertical rows, one one either side of the stem; leaves with parallel veins or only a central vein, the base of the leaves forming sheaths wrapped around the stem nodes, edges of leaves with no teeth or only a few toward the leaf tip.

Flowers small and inconspicuous, unstalked, in two rows on the midrib of one side of a flattened, linear leaf-like spike (spadix) which is hidden in a long slender sheath-like base of a leaf (spathe). Each flower produces pollen or seeds but not both, the pollen-producing flowers typically alternating in each row on the spike. No petals or sepals. Pollen-producing flowers each with 1 stamen that has no stalk, only the pollen-producing structure (anther); falling off soon after flowering. Seed-producing flowers with 2 carpels, fused to form 1 pistil; stigmas 2, long and bristle-like, fused at base, falling off soon after flowering. Fruit achene-like, often beaked; containing 1 seed.