Local botanist John Swindells writes:
In late July, while in Victoria Park I noticed an unusual submerged plant growing in East Lake. A quick look revealed tiny bladders within its feathery leaves, and I realised it was a bladderwort, a plant I’d not seen in London before. As my grandson was with me, I didn’t have time to examine it closely or collect a specimen. There are several British species, which are difficult to tell apart, but all of them are very rare in and around London.
A return visit in August revealed large quantities of Bladderwort around the south side of the lake, and several patches were in flower. I collected specimens and was able to identify it as Bladderwort (Utricularia australis). This is the first ever record in Tower Hamlets, and indeed the first in inner London. The nearest place it has been seen in recent years is in Epping Forest (see a map of its British distribution here). Aquatic plants such as Bladderwort often get moved around on the feet of water birds, and that is probably how it reached Victoria Park.
Bladderworts are one of the very few groups of carnivorous plants that are native to Britain. They live in ponds and lakes, with their feathery, much-branched stems and leaves always beneath the surface, and only the yellow flowers emerging from the water. They capture small organisms by means of bladder-like traps – hence their English name. Prey include water fleas (Daphnia), nematodes and even fish fry and mosquito larvae.
Despite their small size, the traps are extremely sophisticated. Prey brush against trigger hairs connected to a trapdoor. The bladder, when “set”, is under negative pressure in relation to the water, so that when the trapdoor is mechanically triggered, the prey, along with the water surrounding it, is sucked into the bladder. Once the bladder is full of water, the door closes again, the whole process taking only ten to fifteen milliseconds. As the ability of the traps to catch prey declines after a few days a bladderwort plant continually produces new ones. About 15,000 are produced by a single plant in a season and altogether they catch 230,000 items of prey. You can read more about these fascinating plants here.
Header photo: Bladderwort in Victoria Park (John Archer)