Greater bladderwort

A carnivore that floats

The greater bladderwort is an aquatic carnivorous plant with no roots at all: it lives floating just below the surface of ponds and still waters, forming long submerged stems that in a single season can exceed a metre. Its leaves are finely divided into thread-like segments and carry hundreds of tiny bladder-shaped traps (the 'utricles'), which give it its name. In summer it sends up erect stalks above the water bearing showy golden-yellow flowers.

Habitat and distribution

It is widespread across much of Europe and Asia, in still, nutrient-poor fresh waters — ponds, marshes, slow channels — where catching small organisms makes up for the scarcity of nitrogen. In winter the whole plant contracts into compact resting buds (turions) that sink to the bottom, to resprout in spring.

Ultra-fast traps

Its bladder traps are a masterpiece of natural engineering. Each bladder, sealed and held under negative pressure by the plant, has a sensitive trapdoor fitted with trigger hairs. When a tiny aquatic animal — a crustacean, a larva, a protozoan — brushes one of these hairs, the door springs open and water, sucked in by the internal vacuum, drags the prey inside in a fraction of a millisecond. It is one of the fastest movements known in the plant world.

Curiosities

Despite its microscopic ferocity, it is entirely harmless to humans. Its prey are minute organisms, invisible to the naked eye. In aquaria or ponds it is grown by enthusiasts as an oxygenating botanical curiosity.

Conservation

The IUCN lists the species as Least Concern. Like all freshwater plants, however, it suffers from the drainage of wetlands and from eutrophication, which alters the nutrient-poor environments it needs.