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 genus of pretty aquatic plants with creeping rhizomes and long-stalked oblong or cordate leaves, and one-leaved stems terminated by a raceme of blue flowers. Perianth somewhat two-lipped. Stamens 6, the upper 3 often sterile. Ovary 3-celled, two cells abortive and the other 1-seeded. Named after an Italian botanist. Natives of America.
1. P. cordata (fig. 259). Pickerel-weed. - A common North American plant, 1 to 2 feet high, desirable for the hardy aquarium. P. angustifolia is a variety with narrow lanceolate leaves cordate at the base, and also smaller bright blue flowers.
Fig. 259. Pontederia cordata (1/4 nat. size.)
These plants should be placed in 2 or 3 feet of water, or they will not bear our winters.