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 or marsh plants with simple radical leaves and leafless flower-scapes. Flowers hermaphrodite or unisexual. Perianth inferior, all the segments or only the three inner coloured, often fugacious. Stamens 6 or 9 or more. Fruit of 3 to 6 or more dehiscent or indehiscent 1- or more seeded carpels. Seeds destitute of albumen. This small order comprises about 50 widely dispersed species. Besides the following there are about half a dozen other British species, the most conspicuous of which are the Water Plantains (Alisma). A. Plantago is the common conspicuous species with erect lanceolate ribbed leaves on long stalks, and a tall panicled scape with whorled branches bearing small fugacious flowers of which the three inner segments are pale rose colour.