BONAP indicates, for the family Alismataceae, 6 genera in the U.S. (Alisma, Baldellia, Damasonium, Echinodorus, Helanthium, Sagittaria); three of these occur in Iowa (Alisma, Echinodorus, Sagittaria).
These 3 genera have in common: wet habitat (marshes and lake shores), green sepals that remain during fruiting, white (occasionally reddish) petals that fall soon after flowering, carpels are distinct—one loculared usually with a single ovum and becoming achenes in fruit.
USDA Plant site: U.S. 5 species; Iowa 3 species.
BONAP site: U.S. 6 species; Iowa 3 species.
VPI site: Iowa 2 species.
See FNA site: