Submersed marine herbs growing wholly submerged at depths of up to 50 m. Three genera with about 18 species. Flowers highly reduced, hydophilous , unisexual, and sessile in two rows along a spadix which is subtended by a spathe . Pollen grains filamentous , up to 2mm long. From the broad perspective of plant evolution, a flowering plant lineage that has returned to the marine home.
Reproductive adaptations are highly specialized.