Before and during flowering, the thin wigeongrass stems usually grow rapidly, producing numerous lateral branches that branch again, and so on, but nearly stemless plants can also occur. Stems are about 1 mm wide and up to 3 m long, but average plant height is probably about 5-20 cm in most temperate waters. Plants have little strengthening tissue and the surrounding water provides support for dense upper vegetation. The proportion of leaf area at various depths reflects adjustments to differences in light regimes caused by turbidity or the presence of other plants. Flowers Wigeongrass produces huge numbers of underwater flowers about 5-6 weeks after the onset of spring growth.
Flowers begin development sheathed inside a pair of subfloral leaves.
After 1-2 weeks, the spike is pushed out of the swollen sheath by a peduncle that grows rapidly in length. Anthers burst and release pollen, aided by gas bubbles that accumulate inside the anther sac. Some pollen is trapped within the inflorescence and some clings to the surface of the gas bubbles. Peduncle form is one of the main characters taxonomists have used to split R. maritima s.l. into separate species. Annual forms have peduncles that are either short, stiff, and straight or loosely coiled, up to 3 dm long, and that are pollinated underwater.