I can add some avian flavor to the pictures of at least one of these
carnivorous plants - the Waterwheel (Aldrovanda vesiculosa).
This plant species is an aquatic trigger plant that is globally threatened.
It is known to occur only in a few wetlands in Australia - along the east
coast, one wetland in Armidale NSW, a few wetlands in northern Australia (NT
and coastal Qld) and (curiously) another in Esperance in south-western
Australia. The same species also occurs in isolated pockets in southern and
eastern Europe, southern and central Africa, east Asia (mostly north-east
India and along the east coast of China). It does not occur in the Americas.
So have shorebirds or waterbirds inhabiting freshwater wetlands, or even
migratory terrestrial birds bathing/drinking in wetlands been responsible
for introducing this plant to different continents that are along their
migratory pathways, or did the plant species once have a more widespread
global distribution, but now occurs as isolated global remnants? If birds
have been vectors involved in the dispersal of the plant species between and
within continents, where did the plant originate and where was it
introduced? The plant grows in water through the spread of vegetative
propagules and parts of the plant could easily be caught on the feet or
other parts of a bird's body and carried to another wetland. In Australia it
grows in slightly acidic shallow water, particularly among spike-rushes
(Elaeocharis spp.). I've been told that the seeds of Aldrovanda vesiculosa
can also survive reasonably long periods of desiccation, so maybe some are
carried in the feathers or on the feet of bird vectors to other wetlands.
Incidentally, a genetic study of global populations of Aldrovanda vesiculosa
is the subject of an honours project at the University of WA this year. The
results of the study may shed some light onto the evolutionary biology of
this species and perhaps pathways of dispersal between continents.
Stephen Ambrose
Ryde NSW
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