>What is the story behind all those infraspecific taxa of Drosera
>rotundifolia?
>(should that be infraspecific taxa OF or WITHIN D. rotundifolia?)
It depends on the taxon you mean. Principally, the present global range of
_D.rotundifolia_ is a rather young one (like those of _D.anglica_ and
_D.intermedia_, both being less widespread, however), indicating a rapid
spread during Pleistocene after having originated somewhere in N America
some time ago (when exactly?). So all known infraspecific taxa outside N
America must be very young, i.e. comparatively little differentiated from
the common ancestor. Surprisingly (or not? ;-)), the taxa known so far do
really fit this theory:
The _subsp.bracteata_ is morphologically related (virtually
indistinguishable) to _D.rotundifolia_ s.str. but the geographic
disjunction between New Guinea (Wissel Lake region, i.e. tropical colline)
and the continuous area of distribution of _D.rotundifolia_ (temperate to
subarctic circumboreal planar-montane) is too large to assume present
"communication" between the two.
Somewhat obscure is the range/status of D.r.var.furcta RUAN (non REGEL nec
DOMIN), which is coherent with the distribution of _D.spatulata_ in China
(i.e. subtropical colline-montane in the SE) but not with that of
var.rotundifolia which is restricted to cold parts (mostly montane) of the
northernmost provinces in China (N Manshuria, N Inner Mongolia). Maybe this
is a (relict) link between _subsp.rotundifolia_ and _subsp.bracteata_,
possibly having suffered some (more recent) introgression by _D.spatulata_
(morphologically, it is much closer to _D.rotundifolia_ and not really
intermediate, however) in China.
The numerous infraspecific taxa described from N America, Europe, and N
Asia (sympatric with the typical form) are all variants without taxonomic
value.
BTW, In HULTENs distribution maps the range in N America includes the US
Gulf Coast states. I do not know reliable records of _D.rotundifolia_ from
there. But as HULTEN does not deal with _D.capillaris_ and _D.brevifolia_,
I assume these records apply to these taxa rather than _D.rotundifolia_. I
think _D.rotundifolia_ does not occur in Cuba.
Kind regards
Jan