Nymphaeaceae is a family of flowering plants. Members of this family are commonly called water lilies and live as rhizomatous aquatic herbs in temperate and tropical climates around the world. The family contains eight large-flowered genera with about 70 species. The genus Nymphaea contains about 35 species in the Northern Hemisphere. The genus Victoria contains two species of giant water lilies endemic to South America. Water lilies are rooted in soil in bodies of water, with leaves and flowers floating on the surface. The leaves are round, with a radial notch in Nymphaea and Nuphar, but fully circular in Victoria.
Water lilies are a well studied clade of plants because their large flowers with multiple unspecialized parts were initially considered to represent the floral pattern of the earliest flowering plants, and later genetic studies confirmed their evolutionary position as basal angiosperms. Analyses of floral morphology and molecular characteristics and comparisons with a sister taxon, the family Cabombaceae, indicate, however, that the flowers of extant water lilies with the most floral parts are more derived than the genera with fewer floral parts. Genera with more floral parts, Nuphar, Nymphaea, Victoria, have a beetle pollination syndrome, while genera with fewer parts are pollinated by flies or bees, or are self- or wind-pollinated. Thus, the large number of relatively unspecialized floral organs in the Nymphaeaceae is not an ancestral condition for the clade.
Horticulturally water lilies have been hybridized for temperate gardens since the nineteenth century, and the hybrids are divided into three groups: hardy, night-blooming tropical, and day-blooming tropical water lilies. Hardy water lilies are hybrids from the subgenus Castalia; night-blooming tropical water lilies are developed from the subgenus Lotos; and the day-blooming tropical plants arise from hybridization of plants of the Brachyceras Casp. subgenus
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