TNX 4 your detailed (and not mythological) discussion. I do agree in the
most points with your views. So for the sake of data compression let me
focus only on a few divergences.
>I believe the flowers MUST carry out a very important role for those
>species or else they wouldn't have developed such morphologically diverse
>flowers, comparing to the Brazilian Drosera at least (which are
>practically all extremely similar).
Flowers can only be important in terms of evolution in species which
produce seed sexually. This is most probably not the case in some species
of SW AU _Drosera_. I do not doubt floral ecology is important in the other
species. I agree that some of the AU species may be sterile or aneuploid as
a result of hybridization events in the past.
> The north and south could've been the first regions to be
>separated by deserts, since we don't find pygmies nor tuberous species
>in the north, meaning these could've evolved after the isolation of the
>2 regions.
First let us define a term: mediterranean. This is used in the following
text as a climatic type found only in extratropical latitudes (around 40
deg of latitude) on the W side of the continents (as a result of global
climate conditions), neighbouring the corresponding coastal deserts at the
more tropical border and the oceanic temperate regions at the more
temperate border. The E border is frequently formed by drier, more
continental steppes or high mountain ranges. Mediterranean regions are
marked by mild, humid winters, and warm, dry summers. Typical examples are
the Mediterranean in S EU, N AF & SW AS, California in N AM, SW AU, S AF,
and C W Chile in S AM).
Almost certainly, the first region to become a desert in AU was the N part
(as soon as it crossed the S tropic). So the now essentially tropical N AU
species could not have existed there before N AU entered the tropical humid
zone *beyond* the desert zone (as soon as AU had moved further N). Thus,
the recent N AU and S AU species of _D._ did have *completely* different
chorological histories: While the S species were formerly widespread in AU
(and a few of them also leaving AU), their range was successively
fragmented and concentrated by the desert successively spreading from NW to
SE (having reached C AU nowadays), the N species could have established
only much more recently, maybe having originated even somewhere outside AU.
It is not at all a surprise that we meet different sets of species in
(tropical humid) N AU and (mediterranean) SW AU.
I do not think the _D.petiolaris_ group (including _D.banksii_:
Lasiocephala) is in any way comparable with subgen. Ergaleium or subgen.
Bryastrum. The first is a rather small and essentially tropical set of
species which have entered the scene comparatively late in the AU history.
The two remaining are presumably older in AU with a pronounced (more
recent) centre of diversity in SW AU.
_D.subhirtella_ PLANCH. (Ann.Sci.Nat.3.ser.9:292, 1848) is a
straightforward Ergaleium from SW AU *with* bulbs/corms (not tubers!). It
is rather unrealted with _D.banksii_ (STIPULES !!!). Perhaps you meant
_D.subtilis_, which is a N AU element (this has no stipules either!).
>The ancestral Drosera in Australia
>surely didn't know their habitats were shrinking and that they faced
>almost certain extinction if they didn't adapt to the new conditions.
I do not believe they knew what awaited them, but one fraction of them had
the time to adapt and prevent extinction, the other fraction is to be
sought somewhere in the fossil record.
There is a tremendous difference between a drier patch in a subtropical
savanna or campo rupestre somewhat distant from a rivulet with your buddies
growing under optimal conditions in direct (insect-) flight distance and a
mediterranean habitat with the desert approaching from one side and your
buddies forced into the ocean on the other side (the ecological conditions
in AU were much more global, involving the whole range of the species).
> You mentioned that Drosera were most likely widespread in
>Australia before the climate got drier, and that later on were reduced to
>the SW, SE, and northern regions of the country. I believe the
>concentration of species in SW Australia shows that the real "boom" in
>speciation occurred in that region when it was already partially or
>totally isolated from the other two regions.
The two statements do not exclude each other. The concentration of the
species in the mediterranean region of AU has certainly created a new
situation in terms of competition and pressure towards adaptive radiation.
Hybridization is a phenomenon frequently observed in regions of this type
of climate. But I still believe the few "escaped" species of wider
distribution are indicative of a greater age of these subgenera (while many
of the recent species in SW AU may still be much younger). For discussion
of N AU v.s.
Certainly, the C Brazilian plateau may have been a "buffer" in the past.
The Andes are, as you have mentioned a rather young system. Interestingly,
no known species of _Drosera_ has managed to establish in the mediterranean
zone of C Chile (apparently, no species except the subantarctic
_D.uniflora_ was able to cross the Andes to the W), which is the only
region in S AM with a climate really comparable to SW AU. This might
indicate that the expansive _D._ species of S AM came from the E after the
Andes were already fold up, so that the Andes (at some peaks higher than
7000 m) formed a barrier to further distribution rather than a "buffer" for
these. However, keep in mind the (few) species which reach the E foothills
or even the Paramos of the Cordillera oriental (_D.colombiana_,
_D.cendeensis_, _D.cf.montana_ in the Yungas of Bolivia), all of which seem
to be (rather recent?) descendants of closely related species in Brasil.
We should consider a further possibility: AU is the one region on this
planet with the largest number of recent sections and subgenera of
_Drosera_. This might indicate a centre of origin of the whole genus (&
family) closer to AU than to S AM (but it could also be a consequence of a
stronger diversification as a result of the climatic changes mentioned).
> To finish off with some hope, an Australian CP'er once told me
>that the soils in W.A. are slightly more radioactive than normal (...)
It is not easy to prove the opposite but I have some serious doubts about
this theory (& al.: e.g. Mu).
Kind regards
Jan