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.
A small order of aquatic herbs with erect floating or immersed leaves. Unisexual flowers pedunculate, emerging from a small spathe. Perianth of 6 segments, the inner 3 usually larger and coloured. Stamens three or more. Fruit inferior, submerged, 1- to 6-celled, dry or succulent. There are two native species of some interest, namely, Hy-drocharis Morsus - Ranae, Frog - bit, and Stratiotes aloides, Water Soldier. The former is a floating herb with orbicular leaves and white flowers, male and female similar, with the inner segments of the perianth larger and crumpled. The latter is a submerged stoloniferous plant with radical long narrow toothed leaves, solitary female and clustered male flowers. Confined in Britain to Eastern England.