[7][8] The family is further characterized by scattered vascular bundles in the stems, and frequent presence of latex, usually with distinct, stellate-branched sclereids projecting into the air canals.

[citation needed] Leaves are alternate and spiral, opposite or occasionally whorled, simple, peltate or nearly so, entire to toothed or dissected, short to long petiolate, with blade submerged, floating or emergent, with palmate to pinnate venation.

[9][10] Flowers are solitary, bisexual, radial, with a long pedicel and usually floating or raised above the surface of the water, with girdling vascular bundles in receptacle.

[11][12] Some species are protogynous and primarily cross-pollinated, but because male and female stages overlap during the second day of flowering, and because it is self-compatible, self-fertilization is possible.

Nymphaeaceae has been investigated systematically for decades because botanists considered their floral morphology to represent one of the earliest groups of angiosperms.

[6] Modern genetic analyses by the Angiosperm Phylogeny Group researchers has confirmed its basal position among flowering plants.

The genus Barclaya is sometimes given rank as its own family, Barclayaceae, on the basis of an extended perianth tube (combined sepals and petals) arising from the top of the ovary and by stamens that are joined in the base.

[21] The genera Euryale, of far east Asia, and Victoria, from South America, are closely related despite their geographic distance, but their relationship toward Nymphaea need further studies.

[22][23][24] The sacred lotus was once thought to be a water lily, but is now recognized to be a highly modified eudicot in its own family Nelumbonaceae of the order Proteales.

Several fossil species are known, including Cretaceous representatives of Nymphaea, as well as fossil genera such as Jaguariba from the Cretaceous of Brazil, Allenbya from the Ypresian of British Columbia,[25] Notonuphar from the Eocene of Antarctica,[26][27] Nuphaea from the Eocene of Germany,[28] Susiea from the Late Paleocene Almont Flora of North Dakota, USA,[29] and Barclayopsis from the Maastrichtian of Eisleben, Germany.

[33] The main job of the Maya rulers during pre-Columbian Mesoamerica was to obtain clean and drinkable water for their citizens during both the wet and dry seasons.

[34] The Maya began to use water lily iconography depicted on stelae, monumental architecture, murals, and in hieroglyphic writing.

[36] It is likely that the Maya ingested these plants to create a non-ordinary state of consciousness, which makes sense because there is a class of opiate alkaloids in Nymphaeaceae.