Plants usually perennial, rarely annual, aquatic or marsh herbs. Leaves in basal rosettes, petioles with widened bases; blades entire. Inflorescences usually paniculate, with whorls of branches, rarely umbel-like or with solitary flowers. Flowers bisexual or unisexual; tepals 6, the outer 3 green, persistent, the inner 3 petal-like, usually soon falling; stamens (3-)6(-many); filaments narrow; anthers with 2 thecae, longitudinally dehiscent. Carpels superior, 3-many, free or united at the base in a whorl or spiral, 1-celled, with 1 ovule; styles apical, lateral or basal. Fruits usually indehsicent nutlets; seeds oblong, with strongly curved embryos, without endosperm.
The family Alismataceae includes about 11 genera and 95 species. It is cosmopolitan in its distribtuion but best represented in the northern hemisphere.