Nelumbo nucifera, also known as Indian lotussacred lotusbean of India, or simply lotus, is one of two extant species of aquatic plant in the family Nelumbonaceae. The Linnaean binomial Nelumbo nucifera (Gaertn.) is the currently recognized name for this species, which has been classified under the former names, Nelumbium speciosum (Willd.) and Nymphaea nelumbo, among others. (These names are obsolete synonyms and should be avoided in current works.) This plant is an aquatic perennial. Under favorable circumstances its seeds may remain viable for many years, with the oldest recorded lotus germination being from that of seeds 1,300 years old recovered from a dry lakebed in northeastern China.

Native to Tropical Asia, and Queensland, Australia, it is commonly cultivated in water gardens. It is also the national flower of India, and Vietnam.

While all modern plant taxonomy systems agree that this species belongs in the genus Nelumbo, the systems disagree as to which family Nelumbo should be placed in, or whether the genus should belong in its own unique family and order.

The lotus is often confused with the water lilies (Nymphaea, in particular Nymphaea caerulea “blue lotus”). In fact, several older systems, such as the Bentham & Hooker system (which is widely used in the Indian subcontinent) call the lotus Nymphaea nelumbo or Nymphaea stellata. This is, however, evolutionarily incorrect. Far from being in the same family, Nymphaea and Nelumbo are members of different orders (Nymphaeales and Proteales, respectively). Adding to the confusion, some sources have used the scientific name Nymphaea stellata for another species called Blue Lotus or nil mānel in Sinhalese,[citation needed] which is the national flower of both Sri Lanka and Bangladesh.

The roots of lotus are planted in the soil of the pond or river bottom, while the leaves float on top of the water surface or are held well above it. The flowers are usually found on thick stems rising several centimeters above the leaves. The plant normally grows up to a height of about 150 cm and a horizontal spread of up to 3 meters, but some unverified reports place the height as high as over 5 meters. The leaves may be as large as 60 cm in diameter, while the showy flowers can be up to 20 cm in diameter.

Researchers report that the lotus has the remarkable ability to regulate the temperature of its flowers to within a narrow range just as humans and other warmblooded animals do. Dr. Roger S. Seymour and Dr. Paul Schultze-Motel, physiologists at the University of Adelaide in Australia, found that lotus flowers blooming in the Adelaide Botanic Gardens maintained a temperature of 30–35 °C (86–95 °F), even when the air temperature dropped to 10 °C (50 °F). They suspect the flowers may be doing this to attract coldblooded insectpollinators. The study, published in the journal Nature, is the latest discovery in the field of thermoregulation, heat-producing, plants. Two other species known to be able to regulate their temperature include Symplocarpus foetidus and Philodendron selloum.