Date: Fri, 28 Apr 2000 09:38:04 From: SCHLAUER@chemie.uni-wuerzburg.de To: cp@opus.hpl.hp.com Message-Id: <aabcdefg1325$foo@default> Subject: Re: Biogeography of Drosera and Pinguicula
Dear Dan,
> I was wondering what is the evidence for dispersal of Drosera or Pinguicula
> from America into the Old World or South America (if I have interpreted
> your post correctly)?
This has been discussed on this list several times already. For those
who came in recently, here is a short summary.
In the case of _Drosera_, some hints can be obtained from the fossil
record. Several pollen types from the European Tertiary indicate that
Droseraceae have been widespread and well-differentiated (with
possibly more generic diversity than found today in the family) here.
With the exception of _Aldrovanda_ (that contained several species in
the past), all these genera perished (NB: _Drosophyllum_ does not
belong to Droseraceae). _Drosera_ is a new acquisition to Europe
appearing in Pleistocene pollen floras. The species known from Europe
(_D. rotundifolia_, _D. anglica_, and _D. intermedia_) are all
widespread in North America. Their distribution in Europe does show
characteristic traits of glacial migration (they are absent from
typically Mediterranean areas, rare and vanishing in lowland areas of
central Europe, more frequent in the mountains, and apparently still
extending their ranges eastwards in Asia: _D. rotundifolia_ is the
fastest species, followed by _D. anglica_ and _D. intermedia_). The
case of _D. anglica_ is particularly interesting from a chorological
viewpoint because this is a hybridogenic species with one assumed
parent species (viz. _D. linearis_) absent whatsoever from the
European flora but native in North America. There is a +/- pronounced
gap in the otherwise circumboreal ranges of all three species in
Siberia. _D. intermedia_, an element that occupies a remarkably
diversified range in America (from the tropics to the subarctic
regions), is restricted to the cooler regions of Eurasia, indicating
that a boreal race of the species has entered the region (presumably
via the north Atlantic) quite recently.
The European _Pinguicula_ species (of which the fossil record is
inconclusive: no species can be identified without doubt) form four
to five distinct groups:
_P. lusitanica_ (subgen. Isoloba) is an oceanic W European Element
with obvious American affinities (_P. pumila_, _P. lilacina_), low
chromosome count, and therefore supposedly a high (Early-Mid-
Tertiary) age.
_P. alpina_ (subgen Temnoceras) is a typically Arctic+Alpine element.
Its origin and differentiation was quite certainly linked with the
Alpidic system (the Arctic partial range must be a recent postglacial
feature because these areas were covered by Ice during the
glaciations). In this context it seems strange that the species is
apparently missing in the Caucasus, while it reappears in the
Himalaya. This tetraploid species did probably originate (from an
unknown stock now probably extinct; its recent relatives _P.
variegata_, _P. algida_, and _P. ramosa_ are certainly - aneuploid
chromosome counts! - derived from rather than ancestral to _P.
alpina_) in the Alps (where it is most widespread and frequent even
nowadays) during Mid Tertiary.
_P. villosa_ (subgen. unclear, perhaps at the base of Pinguicula) has
a low chromosome count and a circumarctic distribution pattern. So
all we can say about origin and dispersal of this species is that it
is probably old but it cannot have originated where it lives now; the
Nunatak theories of survival of Arctic endemics in non-glaciated
Arctic refugia have +/- all been ground to dust by recent genetic
investigations demonstrating that most of these elements are recently
introduced or hybridogenically originated neoendemics. True European
palaeoendemics did only survive in refugia (high mountains, islands,
gorges, selective soils or habitats etc.) of temperate (S of ca. 50
deg lat) or mediterranean climate. Probably _P. villosa_ has been
distributed widely even before Pleistocene, and it could therefore
have been the stock from which the most differentiated group of
European _Pinguicula_ species (viz. sect. Pinguicula) originated.
Section _Pinguicula_ was certainly born in Europe (only here, three
diploid representatives survived, the tetraploid stock derived
therefrom is centered in Europe). The relict diploids in S Spain
(_P. nevadensis_) and on the island of Corsica (_P. corsica_) are
textbook examples of palaeoendemics. The tetraploid stock of
assumedly intermediate age (Late Tertiary) is most diversified in
Europe, extending towards W Asia (_P. balcanica subsp. pontica_) and
Ireland and N Africa (_P. grandiflora_), with lots of endemic taxa in
the high mountains of Europe. The nowadays circumboreal, octoploid
(Pliocene/Pleistocene?) _P. vulgaris_ (from which the likewise
octoploid _P. macroceras_ seems to have derived in the
circumpacific region) has doubtlessly originated from this tetraploid
stock (e.g. from the Alpine _P. leptoceras_?).
The _P. crystallina_ complex is aneuploid and probably of rather
recent (Late Tertiary) hybriodogenic origin. This characteristically
E Mediterranean element may be polyphyletic (in the sense that two
different evolutionary lines, one from subgen. Isoloba - or
Temnoceras? - and one from subgen. Pinguicula may have been
involved in the primary hybridization event).
These five groups sketched above can therefore be reduced to three
independent lines: 1. Subgenus Isoloba, represented by a single species
in Europe and by several dozens of species and a number of sections in
Central America, making an American origin (not only many species but
also many assumedly primitive species live here) more than likely. Its
exact age and migration route remain somewhat obscure. But it is
probably old and it must have crossed the Atlantic eastwards.
2. Subgenus Temnoceras, likewise represented by a single species but
without close American relatives and with obscure phylogenetic origins,
probably in Mid-Tertiary in Europe.
3. Subgenus Pinguicula, perhaps derived from the nowadays
circumarctic _P. villosa_ or more likely from its ancestors. It is
difficult to trace the exact affinities of this line but considering
the morphological parallels to the entirely Central American sect.
Orcheosanthus and to some of the Cuban species _P. jackii_ and
_P. benedicta_ (that should probably form a group of their own), an
American origin can be imagined here as well.
So with the exception of _Drosophyllum_ (which has tropical W African
affinities close to _Triphyophyllum_, Dioncophyllaceae), _Aldrovanda_
(a typical, very old - Cretaceous! - Old World genus), and some
probably hybridogenic, possibly young aquatic _Utricularia_ species,
all recent European cps seem to have North American (incl. Central
America) ancestors.
Kind regards
Jan
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