Nymphaea 'Sioux': The 6-inch flowers of this changeable waterlily open with yellow flowers that become apricot and then orange. Waterlilies are rhizomatous aquatic plants with about 50 species occurring in the wild, mostly found in the tropics of the Northern Hemisphere. They are characterized by round notched leaves that lie flat on the water, and flowers with numerous petals produced at the end of a long lax stem and floating just above the water surface. In the center of each flower is a cluster of showy stamens. Waterlilies have been cultivated since at least 2,000 B.C. and are divided into hardy hybrids, tropical day-blooming and tropical night-blooming. Waterlilies need full sun to flower and need to be anchored in mud as they are not free-floating.