Secondly, what most people don't seem to know is that Brazil is NOT
totally covered by rainforests and this is NOT because they've all been
cut down either. Northern Brazil, yes is covered by rainforest, as are
the coastal mountain ranges in eastern Brazil. Most of the interior of
the country is covered by savanna, which we call cerrado. We also have
caatinga vegetation in the northeastern part of the country, which is a
very dry region with thick, low, prickly plants mostly. Then there is
also campo rupestre vegetation, which is what you find on the mountain
ranges around the country, including on top of the famous tepuis on the
border between Brazil, Venezuela, and Guyana. There are yet still a few
more types of vegetation in Brazil, which I won't go into.
Anyways, our cerrado and caatinga vegetation are very similar to
what grows in Australia. Our cerrado is like the southern parts of the
Australian continent, with a definite wet/dry season and also
winter/summer, while caatinga is like northern Australia, having wet and
dry seasons, but not really having winters (only caatinga is somewhat
drier I believe). Again, Brazil is NOT hot and stuffy all over. Looking
at a map, you'll see the southern parts of the country are not even in
the tropical zones. Winter temperatures in Australia are very similar to
the ones in southern Brazil, not as cold as most of you are used to. We
get occasional frost and even snow in winter. Cerrados, found in the
interior of Brazil, have slightly milder winters. On the mountain tops,
where campos rupestres abound, it also gets pretty cold and on a few
peaks it even snows. In campos rupestres, like in cerrados, there is also a
definite dry season, which coincides with winter.
What I observe here is that CPs always grow by perennially wet seepages
or by streams which don't dry out in winter. Yet we also have annual
species which survive in habitats which are only humid during the wet
season. So if the habitats are so similar, why did they only evolve weird
ways of life in Australia? You see? What gave those plants the extra
push in Australia to invade the habitats that dry out in the dry season
(which over there is in the summer) and develop mechanisms to survive as
perennials? And why didn't it happen here in Brazil?
I don't think they didn't specialize here in Brazil because the
habitats they live in were "fine" for Drosera. Something is keeping
them from competing with each other here in Brazil and/or with other
plants and thus keeping them from specializing. The Drosera boom is
present in southwestern Australia, but not in the southeastern part of
that country. What's the difference between these regions? What does one
have that the other doesn't? There is a secondary and lesser boom in
northern Australia. Why? Why didn't the CPs in W.A. just stick to those
perennially wet habitats like where Cephalotus and D.hamiltonii grow?
If I remember well, 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
zone. Thus the habitats suitable to the primitive Drosera (probably
similar to the remaining D.spatulata and the species found in S.America)
were almost completely wiped out and maybe this is what gave the plants
the push to specialize. Though again, why it occurred in SW Australia and
not SE, I don't know!!
Fernando Rivadavia
Sao Paulo, Brazil
P.S.
> Do you know, if the habitats of Drosera, Genlisea ... are quite the same
> as at the sandstone-regions (Guyanas) in Venezuela? Do you know, if there
> is a high degree of endemism at the sandstone-regions of Brasil?
Like I said above, Joachim, the plant families and genera on these
sandstone highlands (campo rupestre vegetation) are all very similar, only
the species really vary. Yes, there does seem to be lots of plant
endemism on the Brazilian sandstone highlands too, including with Drosera,
Utricularia, and Genlisea. Only here they're not isolated escarpments, as
in Roraima, but most often continuous mountains ranges. So the taxons are
seen to be endemic to regions, and not separate tepuis.