News published: 11 March 2024

Royal Rotterdam Zoological & Botanical Gardens are conducting a project on Nymphaea thermarum and are trying to create the best guideline possible for the propagation of the plant.

Background

In 2019, the botanical department of Rotterdam Zoo received seeds of Nymphaea thermarum from Hortus Botanicus Leiden. In 2009, the Miniature Rwanda Water Lily was defined as ‘Extinct in the Wild’ on the IUCN Red List. It was orginally described in 1987 based on observations at an amashyuza (hot springs) area, at 1100 m by Dr. Eberhard Fischer.

We realized that this species could have a very valuable message to the public describing the role of botanic gardens in conserving endangered species and saving them from the brink of extinction. Our ex situ plants could serve as an ambassador for future in situ projects. Seeds of the species were sown using the methods in the publication of Carlos Magdalena Rodriguez published in Curtis’s Botanical Magazine 2010 vol. 27 (4): pp. 318–327.

The results of the first attempts to propagate this species from seeds worked out very well. Many seedlings were raised and finally, 12 adult F1 accessions were potted in our nursery. The plants grew well and their condition was good and flowers were produced. Seeds were collected and attempts to breed the next F2 generation failed over and over, despite using the same methods, materials, and circumstances to breed the generation before.

We are eager to identify the issue and solve the problems to avoid the loss of our F1 generation. We observed very different conditions of the plants. Adaptions and changes of our temperate season seem of major influence on the condition of the plants. During winter the plants look weak and poor, even using artificial daylight. Changing the water level from moist to submersed in combination with adding regular fertilizer for aquarium plants, seems to work. Flowering plants appeared again in early summer and seeds were produced. However, seedlings, were covered by algae using the ‘old method’ and the leaves of young plants still turn out weak and fluffy. Young plants continued to develop in adult flowering plants and a lot of die-off occurred in the nursery setup.

At some level tide was changing in the spring of 2023. Due to the persistence of our senior gardener, several attempts to propagate N. thermarum were continuously undertaken resulting in healthy seedlings and 4 juvenile plants. Furthermore, more than 10 samples with hundreds of seeds could be collected and stored in the fridge in a bottle with distilled water.

The whole process of ‘trial and error’ over the years to cultivate some plants by using different horticultural aspects (sometimes in contrast with literature and methods of other institutions), raised the question of writing a complete guide for the best practice to raise the numbers of this critically endangered plant species. The aim of writing this guideline could focus on the following aspects, problems, unclarities, and methods used by others, to collect as much data and knowledge as possible.

If you would like to take part in this questionnaire please follow the link.