Plants either apocarpous and sometimes monocarpous flowers or more or less aquatic, often both and always herbaceous but never thalloid. The taxon has trinuceate pollen, rather than binucleate pollen and therefore the Alismatidae is not on the main branch of monocot evolution but represents a relictual side-branch. Summary from the University of Wisconsin Alismatales Dumort. Aquatic or wetland herbs with bisexual flowers with 3 green sepals and 3 petals bearing an apocarpous gynoecium with many free carpels resulting in a spiral or ring of achenes. Cosmopolitan, especially in north temperate regions.
Pollen often multiporate.
An important group for waterfowl. Many fresh-water species are important for fish and waterfowl habitat. Egeria and Elodaea are sometimes cultivated for use in fish tanks. Thalassia and Halophila are marine genera with pollen in thread-like chains. Cosmopolitan, mostly in temperate regions.