Nymphaea lotus var. thermalis

Nymphaea lotus var. thermalis is a water lily which blooms at night[2] – its flowers last four days and have four sepals, 19–20 white petals along with yellow anthers and stamens.[3] There is usually a 15–30 cm gap between flowers and the surface of the water, flowers are slightly fragrant; the round leaves of the plant are 20–50 cm wide.[3] A description was first formally published in Math. Természettud. Értes. 25(4):32, 36. 1907.[1]

Nymphaea lotus var. thermalis is endemic to the thermal water of the Peţa River, Sânmartin, Bihor County, Romania.[2] The area is protected as a nature reserve (51.0 hectares (126 acres) in size) and consists of a rivulet along with three ponds. The water has a roughly constant temperature of around 30 °C whilst the site has an average air temperature of 10–11 °C.[2] The thermal waters have been recorded as early as 1211, but it was only in 1799 that the first record of N. lotus was made, by Pál Kitaibel.[2][4] Janos Tuzson proposed in 1907 that this population's unusual location could be explained by the persistent heat provided by the thermal springs could have sustained the population at a pre-ice age time when the plant would have been spreading across the warmer regions of Europe; this theory was corroborated by additional evidence provided by the identification of other endemic species.[2][5] Alexandru Borza was the Government minister in charge of education (and also a botanist) who made the first push for legal protection and recognition of Nymphaea lotus var. thermalis – in 1932, the Cabinet of Romania declared the rivulet a nature reserve and the plant a "national monument".[2] Conservation action with the intent to preserve this population has been undertaken for many years (since at least 1940) – including the management of invasive species – and the plant has been included in recent water management legislation.[2]

Whilst not held in any Romanian botanical gardens, Nymphaea lotus var. thermalis is grown at Royal Botanic Gardens Kew and at the botanic garden of Bonn University.[2]