Barclaya Wall. (4 spp.) Euryale Salisb. (1 sp.) Nelumbo A. Rich. - water lotuses (2 spp.) Nuphar Sm. (9 spp.) NymphaeaL. - water lilies (47 spp.) Ondinea Hartog (1 sp.) Victoria Lindl. - giant water lily (2 spp.)
The Nymphaeaceae (water lilies) belong to the Order Nymphaeales. They are tuberous plants that are rooted in soil in bodies of water, with leaves and flowers floating on the water surface. Some species of the water lotus are used as food.
Modern phylogenetic thinking about the flowering plants regards the water lilies as the most basal ("primitive") of the flowering plants.
Many botanists place the genus Nelumbo in its own family, the Nelumbonaceae.
A lotus can be a water lily in either the genus Nymphaea (the Egyptian lotuses) or Nelumbo (the Indian lotuses). Like most water lilies, both plants have round leaves that float on the surface of the water. Nymphaea leaves have a radial notch, while Nelumbo leaves are peltate, meaning they have no notch reaching into the petiole (leaf stem). Nelumbo fruit is often used in flower arrangements. It has about twenty pits in its upper surface, each of which contains a seed. Both plants have been used as religious symbols.
Nelumbo nucifera is highly regarded in Hindu and Buddhist cultures and has been given the status of National Flower of India. This species is also edible in all its parts and is used in many Asian cuisines.
References
Nymphaeaceae Salisb. (1805) - R. A. Salisbury, in the Annals of Botany (Editors C. König and J. Sims), 2:70. London, 1805.
L. Watson and M. J. Dallwitz (1992 onwards). The Families of Flowering Plants - Nymphaeaceae (http://biodiversity.uno.edu/delta/angio/www/nymphaea.htm)
Nelumbo, the Indian lotus, has peltate leaves
Nymphaea colorata from Africa is a member of the Nymphaeaceae
Modern genetic tests of the flowering plants by the Angiosperm Phylogeny Group have shown that the waterlilies are among the most basal ("primitive") of the flowering plants.
Hardy waterlilies bloom only during the day, but tropical waterlilies can bloom either day or night, and are the only group to contain blue-flowered plants.
Among the plants of the family are the waterlilies, lotuses, and pond lilies (called also cow lilies and spatterdocks) of the genera Nymphaea, Nelumbo, and Nuphar, respectively; however, the common names often overlap; e.g., "waterlily" is used for most species of the family and even for other unrelated aquatic plants with similar flowers.
Many members of the waterlily family have seeds or tubers that have been used for food; however, the fruit of the lotus-eaters of classical literature has been most often identified as that of the jujube of the buckthorn family or the nettle-tree of the elm family.