Lotus. Nelumbo is a genus of aquatic plants with large, showy flowers. Members are commonly called lotus, though lotus is a name also applied to various other plants and plant groups, including the unrelated genus Lotus. Members outwardly resemble those in the family Nymphaeaceae, but Nelumbo is actually very distant to Nymphaeaceae. There are only two known living species of lotus; N. nucifera is native to Asia and is better-known. It is commonly cultivated; it is eaten and used in traditional Chinese medicine. This species is the floral emblem of both India and Vietnam. The other lotus is Nelumbo lutea and is native to North America and the Caribbean. Horticultural hybrids have been produced between these two allopatric species. There are several fossil species known from Cretaceous, Paleogene and Neogene aged strata throughout Eurasia and North America. Nelumbo lutea; American lotus. Nelumbo nucifera; sacred or Indian lotus, also known as the Rose of India and the sacred water lily of Hinduism and Buddhism. It is the national flower of India and Vietnam. Its roots and seeds are also used widely in Asian cooking. Nelumbo aureavallis; Eocene, described from leaves found in the Golden Valley Formation in North Dakota, USA. Nelumbo changchangensis Eocene, described from several fossils of leaves, seedpods, and rhizomes from the Eocene-aged strata in the Changchang Basin, of Hainan Island. Nelumbo minima Pliocene, described from leaves and seedpods that suggest a very small plant. Originally described as a member of the genus Nelumbites, as Nelumbites minimus. Nelumbo nipponica Eocene-Miocene, fossil leaves are known from Eocene-aged strata in Japan, and Miocene-aged strata in Russia. Nelumbo orientalis Cretaceous, one of the oldest known species, fossils are found in Cretaceous-aged strata of Japan. Nelumbo protolutea Eocene, fossils of leaves strongly suggest a plant similar in form to the American lotus. There is residual disagreement over which family the genus should be placed in. Traditional classification systems recognized Nelumbo as part of the Nymphaeaceae, but traditional taxonomists were likely misled by convergent evolution associated with an evolutionary shift from a terrestrial to an aquatic lifestyle. In the older classification systems it was recognized under the biological order Nymphaeales or Nelumbonales. Nelumbo is currently recognized as the only living genus in Nelumbonaceae, one of several distinctive families in the eudicot order of the Proteales. Its closest living relatives, the, are shrubs or trees. The leaves of Nelumbo can be distinguished from those of genera in the Nymphaeaceae as they are peltate, that is they have fully circular leaves. Nymphaea, on the other hand, has a single characteristic notch from the edge in to the center of the lily pad. The seedpod of Nelumbo is very distinctive. The APG IV system of 2016, recognizes Nelumbonaceae as a distinct family and places it in the order Proteales in the eudicot clade, as do the earlier APG III and APG II systems. The Cronquist system of 1981 recognizes the family but places it in the water lily order Nymphaeales. The Dahlgren system of 1985 and Thorne system of 1992 both recognize the family and place it in its own order, Nelumbonales. The USDA still classifies the lotus family within the water lily order. The leaves of Nelumbo are highly water-repellent and have given the name to what is called the lotus effect. Ultrahydrophobicity involves two criteria: a very high water contact angle between the droplet of water and the leaf surface, and a very low roll-off angle. This means that the water must contact the leaf surface at exactly one, minuscule point, and any manipulation of the leaf by changing its angle will result in the water droplet rolling off of the leaf. Ultrahydrophobicity is conferred by the usually dense layer of papillae on the surface of the Nelumbo leaves, and the small, robust, waxy tubules that protrude off each papillae. This helps reduce the area of contact between the water droplet and the leaf. Ultrahydrophobicity is said to confer a very important evolutionary advantage. As an aquatic plant with leaves that rest on the water's surface, the genus Nelumbo is characterized by its concentration of stomata on the upper epidermis of its leaves, unlike most other plants which concentrate their stomata on the lower epidermis, underneath the leaf.