Biological flora of Central Europe: Aldrovanda vesiculosa L

Aldrovanda vesiculosa L. (Droseraceae) is a very rare and critically endangered submerged aquatic carnivorous plant with snapping traps which grows in shallow, standing dystrophic waters such as: lakes, dam reservoirs, peaty fishponds, pools in peat bogs and fens, backwater pools and oxbows in floodplains and basins of large rivers. While it covers a vast territory of four continents in the Old World across various climatic zones, its recent natural fragmentary spread includes only around 50 sites worldwide following a marked population decline during the last 150 years. The major extant world sites occur in Ukraine, Poland, Romania and W Russia. The plant exhibits a marked physiological polarity along its linear shoot with rapid apical shoot growth. Flowering and especially seed-set are rare and stimulated by high temperatures, yet the plants propagate mainly vegetatively by branching. Seeds probably form a seed bank and colonise new sites by being transferred by water birds. All temperate and some (sub)tropical populations form winter buds (turions), which sink to the bottom in autumn and actively rise to the water surface in spring. The world population of Aldrovanda is genetically rather uniform which may be caused by at least one recent bottleneck followed by long-distance dispersal by water birds combined with the founder effect, low mutation rates and dominant asexual reproduction. Aldrovanda is stenotopic and although it is relatively tolerant of many individual ecological factors, it requires an optimal combination of many ecological habitat factors and even small changes in this combination can lead to its decline or extinction. The most important ecological requirements are: high CO2 concentration in the water ( > 0.1 mM), shallow water of at least 0.1 m, habitats free of dense stands of either submerged, free-floating or emergent plants or filamentous algae, a thick layer of slowly decomposable plant litter on the bottom and abundant zooplankton as prey. The main threats to its sites are water eutrophication and water level decline. The introduction of Aldrovanda to potentially suitable sites has become an efficient way to conserve its endangered world population in Switzerland, Poland, Czech Republic, The Netherlands, Australia and Japan.