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Carlos Magdalena >

Nymphaea thermarum was discovered in 1987 by Professor Ebehard Fishcher in Rwanda, Central Africa, at Mashyzuza near Nyakabuye. This unusual Nymphaea species is a taxon that ticks all the boxes in “my personal choice” plant check list. Let’s go point by point.

Conservation status - Known from only one country and one location, you can’t get more endemic than this. There are some reports that state that the whole world’s population is around 50 specimens. Hence it is vital that that we learn how to grow and propagate this species to preserve it ex situ and if possible to store seed in a seed banking facility as insurance for the worst than can happen.

Horticulturally speaking, it’s difficult to grow - This species has been growing for many years at Botanische Gärten Bonn, Germany. It doesn’t seem to form tubers and seeds seem nearly impossible to bring to maturity. There is a challenge. Good!

Rarity - One location in the wild and one single botanic garden growing it should speak for itself.

Oddity - To me this is a really unusual species. So far, none of my specimens has developed a spread that surpasses 10cm (4”). I guess that they will get larger than that but I can’t recall any Nymphaea species that flowers at such a tiny spread.

Despite being a tropical day bloomer placed amongst the Nymphaea subgenus Brachyceras, the leaves are typical of a Nymphaea subgenus Nymphaea. There are no markings on the undersides; they are almost perfectly round with a totally smooth margin, no teeth at all; petioles are shorter than the leaf blades. Sepals (which are a bit hairy …) seem to be as large as flower petals. The plant doesn’t seem to form tubers; seeds are quite large for a Nymphaea subgenus Brachyceras and dark black in colour. Surely, these abnormalities must come as an adaptation to:

An unusual habitat. It doesn’t grow in a lake; it doesn’t grow in a river; it doesn’t grow in a marsh or in a bog or small pond. Where does it grow? This species grows in a thermal hot spring. It is the only place where it can be found.

Scientific interest - If you agree with all the above, you surely agree that this species is of high scientific interest.

Breeding potential - Well, I really do think this little plant can change the face of tropical hybrid production. So many unusual traits could be added into the hybrids’ gene pool and this can’t be bad at all. The only down side I can see is the very low petal count, but if some of the hybrids are not sterile, which seems quite likely, this can be surely fixed at a later day. Yes, you just guessed it … I plan to use it! So far the priority is to reproduce the true species, a must given the conservation importance, but once this is done … why not? Watch this space …   

Seeds of Nymphaea thermarum germinate very easily. However, if grown like any other Nymphaea they simply don’t grow. I was sent seeds from Bonn Botanic Gardens once and none of the many seedlings got anywhere. This was very frustrating. I tried to gather as much info as I could (not much!). Not being able to communicate with anybody that has seen it in the wild was a constraint. Then I found this.

“Eine sehr seltene und endemische Art.

“Nymphaea thermarum wurde erst 1987 von Prof. Dr. Eberhard Fischer entdeckt und konnte bisher nur in der heissen Quelle (40°) Mashyuza bei Nyakabuye nachgewiesen werden. In den Abläufen dieser Thermalquellen wächst Nymphaea thermarum bei ca. 24 bis 26° C Wassertemperatur.”

Believe it or not, this is great. Oh yes, a small detail. This is great if you translate it from the German. One of our Kew Diploma students, Felix Merklinger; did a translation from this text for us now to enjoy …

“A very rare and beautiful species.

“Nymphaea thermarum was only discovered in 1987 by Prof Dr Eberhard Fischer and is so far only known from the hot springs (40C [104F]) Mashyuza near Nyakabuye. In the overflows of the springs (I guess he means where the water drains from the hot springs in little channels), Nymphaea thermarum grows at approximately 24-26C [75-79F] water temperature."

This gave me a few clues:

It then doesn’t need to be grown in piping hot water
The quotation provides a temperature where it naturally grows.

Then I thought … which possible parameters can affect the seedling growth?

Temperature - seems specified at 24-26C (75-79F), but it may worth trying different ones such as 30-32C (86-90F)

Nutrients/compost - Loam? Loam + food? Peat/sand? In the case of using the first two, you can almost predict for sure that you will have hard water, especially in a small tank, and high electric conductivity.

pH, hardiness, electrical conductivity - those usually tie up together: hard-alkaline-high electrical conductivity or soft-acidic-neutral to low conductivity.

And then the Achilles heel of the submerged aquatics: CO2.

I can control all of those at Kew. All but one: CO2.

Then I thought about asking for more seed and running a trial. Two different temperatures: 23/24C (73/75F) and 30/32C (86/90F). Two different water qualities: hard and soft. Two different media: a rich loam and a peat/sand for the acidic conditions.

They didn’t like it, especially the warmer conditions and, for the worst, the warm low nutrients. So there was a conclusion here. It doesn’t like it that warm, at least as seedlings, and acidic soft water does not do much for them either. So it seems like it may need CO2 but I don’t have a CO2 injector. How could I overcome this? I thought … well, if oxygen dissolves more at the surface of the water (the reason behind of fish constantly surfacing in hot/anoxic conditions…) CO2 may do the same. Then I remembered the staff in Bonn said that it likes it shallow. Then I re-read the German paragraph and tried to imagine the conditions … and the overflows and the little channels and I thought - eureka!!!! What about keeping them so shallow that they actually touch the air surface?  

I re-sowed the seeds, some in a pot in water 1mm (.04”) deep, others in totally soaked and undrained damp loam. For the ones in damp loam, I suspected that if they dried on the surface for a second they would go crispy, so I placed them inside the misting unit so they stayed in 100% humidity.

It worked! The ones that were 1mm (.04”) deep started to grow leaves that were submerged in shape but touching the surface. The ones that were in the loam did the same, but as they were out of the water they were smaller but thicker. Amazingly for those in damp loam, the first filiform leaf grew erect and totally out of the water, just like a blade of grass does. The hastates and following leaves became something like “floating in mud” leaves.

Then I decided to try a third thing -- to transplant a few of the seedlings from both locations into damp loam in a pot that was placed in a water-retaining container that was filled with water to the very same level as the loam in the pot. This was then placed on a heating mat at 24C (75F), in a very bright light location, brighter than the two previous experiments. Every single plant grew even better as you can see in the pictures with this article.

Remarkably, I could observe that the meristem of this species is sunken in the mud, probably an adaptation to the no water/shallow conditions where it lives, to prevent dehydration in the very early stages of leaf development.

Did I just mention the word imagination? Can I then use it and even get carried away by it? Here I go … 

Evolution wise … despite their totally aquatic range at present, Nymphaeales evolved on land and then made it into the water. The terrestrial members became extinct and the aquatic ones originated the waterlilies.

Now … is N. themarum a terrestrial waterlily making its way into the water from a terrestrial ancestor and hence a very primitive member of the family, or somebody getting out of the water, making it one of the most “adventurous” species that is making the terrestrial “leap” once again. Given its difficulties when growing underwater, I’m inclined to think that it is getting in the water, but was a Nymphaea the genus that first made it into the water? I doubt it … but for sure we can use our imagination to figure this out (well yes, and DNA studies, analysis of fossil basal Angiosperms, micromorphology applied to evolutionary science, and many other amazing research techniques may help, indeed!!!).

Horticulturally … Could this species enable us to obtain hybrids that grow out of the water and are compact enough to grow in a bowl of wet loam? In what colour would you like your hanging basket with a semi-epiphytic waterlily next summer? And when we thought that we have seen them all ...

Special thanks to Botanische Gärten Bonn for providing the seeds to RBG Kew.