Regarding your continental drift and climate change hypothesis,
basically what you mentioned was that Drosera originated somewhere in
Gondwana who knows how many million years ago and that the present-day
Drosera diversity is a result of the speed at which and the direction in
which each piece of Gondwana drifted. India moved too fast on its way
north to Asia and the local species didn't have time to adapt, thus
being extinguished. Australia moved at a speed sufficient to allow
diversity to occur and help push it along. Africa moved slower and not
as far north, thus there wasn't as much pressure to diversify as in
Australia. While S.America moved mainly west and the Andes mountains
served as a "buffer" habitat for Drosera, allowing them to simply
migrate north or south (or from lower to higher altitudes and vice
versa) along this range when climates changed.
What I'd first like to comment on this is that if this buffer
really did exist, it could actually have been the mountain ranges in
Brazil, which extend from the southernmost tip in Rio Grande do Sul
state to Bahia and Mato Grosso states. The reason I'm saying this is
because various Drosera species are known from the Brazilian highlands
today, yet I can't think of any that grow in the Andes, except for
D.uniflora in the extreme south (Tierra del Fuego, southern tip of
Argentina and Chile) and D.ceendensis (northwestern Venezuela).
The mountain ranges in Brazil (up to almost 3000m in altitude)
are not as high as the Andes are nowadays (I think up to around 6 or 7
thousand meters, I'm not sure) of course, but by what I know the Andes
are a fairly recent formation and began rising as S.America began
drifting west. Maybe both the early Andes and the Brazilian mountains
ranges (and maybe even the Roraima Highlands) were acting together in
this buffer process, but then as the Andes got higher and drier the
local Drosera species could've become extinct.
(to be continued)
FERNANDO RIVADAVIA
Sao Paulo, Brazil