This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Aquatic herbs easily recognised by their large flat cordate or peltate leaves and showy flowers. Sepals 3 to 5. Petals 3 to 5, or numerous, sometimes small. Stamens many. Carpels 3 or more, in one whorl or series, adnate to a fleshy disk forming a several-celled ovary; styles equal in number to the carpels; stigma peltate or decurrent; ovules many, scattered over the walls of the cells; ovules orthotropous. Fruit with consolidated or free carpels; seeds numerous; albumen farinaceous. Fresh-water plants, not numerous in species, but very widely spread. The hardy species are limited to our well-known white and yellow Water-Lilies, with a few others from North America and Siberia.