Nymphaea thermarum 

Before becoming extinct in the wild, Nymphaea thermarum occurred in Mashyuza, southwest Rwanda (Africa). At present all the extant plants are in cultivation at Kew and in Germany.

Nymphaea thermarum in cultivation at Kew (Image: Andrew McRobb, RBG Kew)

A tiny waterlily, forming rosettes 10-20 cm wide and comprising bright green lily pads (laminas) with short petioles. The lily pads can be as little as 1 cm in diameter. The central growing tip sinks in the wet mud, preventing the developing pads from drying out before unfurling.

The flowers are white with yellow stamens, and can be self-pollinating. Blooms open early in the morning and close in early afternoon. The flowers are held vertically, a few centimetres above the plant, but once they have finished their flowering cycle the petiole bends so that the fruit is in contact with the damp mud. Once it is mature, the fruit dissolves releasing the seeds. Reproduction is by seed only.

The only population of this species has died out as a consequence of over-exploitation of the aquifer that fed the hot spring that kept the plants moist and at a constant temperature.

However, since this species is now easily propagated and cultivated at Kew, and the spring water is still flowing (but sequestered before it reaches the surface), there could be an opportunity to restore the site and reintroduce Nymphaea thermarum to Rwanda.

This species has always been so rare that no uses have ever been known. However, Nymphaea thermarum could have potential as a parent for ornamental hybrids, with the benefit of producing tiny plants that do not need a pond to grow and bloom. Some other species of waterlily are used locally as a source of food, such as Euryale ferox seeds in Asia and some Australian species that are commonly consumed by Aboriginal populations. However, some of the approximately 50 species of waterlily are toxic if large quantities are eaten.

This is an unusual waterlily species, as it does not grow in deep water. A small plant pot should be filled to the top with fine loam, and then placed in a water-tight container which is wider and slightly higher than the pot. The container should then be filled with water to exactly the level of the top of the pot and soil. Once the soil is damp and has settled, it should be removed from the water-tight containers and then seeds can be thinly sprinkled on to the surface. The water level is crucial (it must not go down more than 2 mm or up more than 0.5 mm), and the seeds must remain wet but very close to the surface so that when they germinate they are exposed to the air. The seedlings should be kept at 22-26 ˚C and the first leaves will then soon be produced. Seedlings should be exposed to full sunlight. Seedlings should be pricked out into individual pots when they are large enough to handle (usually when there are five leaves of 5 mm in diameter). A few months later the flowers should appear.

There are over 50 Nymphaea thermarum plants in the Living Collection at Kew, which is the only place in the world where it is being propagated regularly and in large quantities.

Aquatic Garden at Kew

Bonn Botanic Gardens (Botanische Garten Bonn)

View images on Victoria Adventure - Nymphaea thermarum

Water Gardeners International - Nymphaea thermarum