Aldrovanda vesiculosa is known as the waterwheel plant, after its traps that whorl out from the stem. The traps are like a Venus Fly Traps, but smaller. It’s also even more endangered than the Venus Fly Trap, and a paper by Lubomir Adamec in Perspectives in Plant Ecology, Evolution and Systematics, highlights how strange that is.
There are plenty of plants with very specific requirements for habitat. Left to its own devices, Aldrovanda vesiculosa insists on living in Australia. Or Asia. Or Africa. Or Europe. It can be found in lakes or rivers, in fishponds or reservoirs. With a range from Russia to the tropics, it should be capable of living in many places, yet there are only fifty verified sites where it lives in the wild. Though it has recently been reported in the Balkans. In fact it appears to be a ‘stenotopic‘ species. It needs quite a few factors to be just right.
As well as having a small population, it’s also not very genetically diverse. Adamec describes it as being nearly a monoclone. The genetic diversity is a problem partly because of how the plant reproduces. It mainly reproduces vegetatively as branches break, leading to genetic uniformity. Adamec says the population went through a genetic bottleneck recently and, when water birds take seeds to new sites, the Founder effect amplifies this genetic uniformity.
There are a couple of threats to the plant’s survival. One is climate change, as you might expect. A warmer climate will mean less rainfall, and less predictable rainfall in some places, leading to wetlands drying up. A. vesiculosa likes at least some water, as it migrates to the bottom of the water in the autumn by forming turions. These are buds that sink to protect the plant from exposure during winter.
The second problem is increasing fertilizer. Fertilization leads to eutrophication, with the excess of minerals providing a food bonanza for algae and causing a headache for carnivorous plants that evolved carnivory to cope with low nutrient habitats.
One method of conservation has been to introduce the plant to new locations. This invasive assistance might sound like a recipe for disaster, but Adamec refers to research showing that A. vesiculosa can be preserved in the USA. He notes that given the travel by bird across Europe, the plant must have an ability to colonise new places if it can find a suitable home. Given people don’t complain about being overrun by waterwheel plants in Europe, it’s probably not that often it can find a habitat that works.
Adamec lists factors that will assist A. vesiculosa conservation, from CO2 concentrations, to water depth, to nutrients, to the broader ecological context for the plant to find new habitats and spread across a landscape.
Adamec concludes with a series of questions we cannot answer yet about ecology and genetics. They’re being researched but, without a wild population, the answers might be a lot less useful.