Speculation on drosera evolution.

Scott Portman (sportman@students.wisc.edu)
Wed, 31 May 1995 11:36:42 -0500

Hi all;

Following up on Fernando Rivadavia's thread on the comparative lack of
Drosera in Brasil compared to Australia...

There's a couple factors I can think of that might cause greater speciation
in one region, more or less independent of climatic or physical

* Perhaps Australian Drosera have developed greater pollinator specificity.
That's one reason why there is such an incredible variety of new world
Orchids, compared to the relative poverty of the African orchid flora.
What pollinates Australian Drosera, and how restricted is the range of the

* Is there a difference in the way most Australian Drosera disperse their
seed compared to those in the rest of the world? Do Brasilian drosera, D.
rotundifolia and other widespread species rely on transport by birds? If
Australian Drosera rely only upon mechanical processes like rain, it could
be that specific species might evolve in isolated drainage basins.
Restricted seed dispersal is one explanation for the diversity of Lithops
and other Azioaceae in South Africa, and might make sense for Drosera as

>Joachim suggested that the harsh aussie climate was
>responsible for the local Drosera diversity and that in Brazil this
>doesn't occur because the habitats are more suitable for Drosera....

>John Degreef mentioned that the genus Drosera
>appeared around 65 million years ago (at the end of the age of
>dinosaurs!), according to pollen fossils.
>I think he even mentioned that
>Australia's changing climate was probably responsible for the local
>diversity, as the continent drifted north from a humid zone to a dry

I'm surprised that Drosera is that old! Over a period of 65 million years,
I suspect the climate in both Brasil and Australia has undergone some
periods of radical climate change. Does anybody out there know whether
western Australia experienced a more disruptive climate over the last few
million years than eastern Australia? Have either experienced more
disruptive climate changes than dry/wet periods in South America?

Both climatic change and stability can result in speciation depending on
circumstances; there are lots of kinds of Sarracenia because local
populations were reproductively isolated during the ice ages, but long
periods of relative stability has certainly produced a rich flora in other
places... Who knows? Climatic change and speciation is a complex matter;
if things were reversed and there were more Drosera species in Brasil, one
might be able to construct a climatic rationale for hyperspeciation there.
Anyone have any other ideas on this?