As regular readers would know, every now and then I come across a plant so compelling I feel obliged to tell its story without ever having laid eyes on it. Today it's a relative of the Sundew (Drosera) called Aldrovanda vesiculosa.
The common name - Waterwheel Plant - caught my attention. I'd just been listening to the Science Show on ABC Radio National, getting the latest on how bacteria evolved their motorised flagella and I though perhaps here was a flowering plant able to spin like a wheel.
It isn't and it doesn't, but what a plant. It consists of a floating stem with traps extending out like a water wheel. These traps work in a similar way to those of the Venus Flytrap, Dionaea muscipula, snapping shut in 1/50 of a second when an insect visitor to trips two hairs in the mature device. Charles Darwin called it the 'miniature aquatic Dionaea'.
There are lots of species of Aldrovanda in the fossil record, but only one living on Earth today. This species, Aldrovanda vesiculosa, has been recorded from Australia, Asia, Europe and Africa. Records are scatted and the species is considered to be at risk of extinction worldwide.
The map of its distribution in Australia shows a species of apparently no particular preference other than aquatic habitats more or less near the coast. It's in the north, the south and even in the south-west - but not (yet) found in Victoria or Tasmania.
As reported by Robin Wylie in New Scientist, habitat destruction and illegal collection (hence the vagueness in locality reports on the web) have meant it is down to 10% of its abundance a hundred years ago. In NSW there is a 'Saving our Species' page dedicated to its survival. There are three existing localities mapped and a fourth site flagged for relocation.
Relocation depends on gathering, storing and germinating seed, and that's yet another problem for the species (outlined in a recent paper in the Botanical Journal of the Linnean Society). A group of mostly Western Australian researchers led by Adam Cross found that only 12% of seeds could be germinated after one year. Most of them succumb to fungal attack.
The seed coat looks smooth but according to this report it has a 'honeycomb-like arrangement' which helps the seed to float but also provides an easy route for fungi to enter the seed.
Freezing kills the seed but cryostorage of actual plants or embryos may be possible. For now though, the authors suggests we protect their habitats and put more effort into finding out what stops Waterwheel Plant thriving in nature.
The Waterwheel Plant is the only aquatic plant with a trap that snaps shut to capture prey. In 1876 Charles Darwin thought this was pretty cool, and went on to show it digested water fleas and mosquito larvae. Unless we care for this plant in the wild, and support some conservation science, a mere (in evolutionary terms) 140 years later we may be witnessing the end of this strange and beguiling plant lineage.
Images: Having not seen this plant myself, these images are not mine. The top two are from Summa Gallicana, the top one originally sourced it seems from Barry Rice's sarracenia.com (who allows the use of his images subject to attribution). The close up of the 'waterwheels' thanks to Lubomir Adamec, from the US Geological Survey. While all the plants illustrated here are quite green, in Australia the Waterwheel Plant is usually reddish in colour, not unlike many of the sundews. Here is another photo by Lubomir Adamec (Carnivorous Plants) of a plant from northern Australia.