Date: Mon, 8 May 2000 11:08:46 +0000 From: schlauer@chemie.uni-wuerzburg.de To: cp@opus.hpl.hp.com Message-Id: <aabcdefg1427$foo@default> Subject: Re: Oldest CP?
Dear Jason & DAVION,
> All this talk of earth ages has me wondering, does anyone have a plausible
> idea of what would be the "oldest" CP in the world? Somewhere I seem to
> recall that some form of Aldrovanda might be the progenitor of the CPs we
> have today but I'd really like to know.
First of all, there is not a *single* progenitor of *all* recent cps.
Cps are derived from at least four *different* lines of flowering
plants. This is very well supported by genetical and phytochemical
evidence, so we do not have to rely solely on morphological
characteristics (which alone would already be sufficient to document
the differences, however).
The oldest known cp fossil (if the attribution is correct!) is a seed
of a possible _Aldrovanda_ progenitor from the Czech Upper
Cretaceous. Nobody can tell how the corresponding plant did look like
or if it was already carnivorous.
> Is there some place scientists can identify as the fountainhead of
> CPs?
Definitely not. The polyphyletic nature of cps quite naturally
necessitates several different places of origin. Migrations and
possibly some cases of long distance dispersal have further covered
the tracks.
> Is there any particular single species
> that gave rise to all others?
Definitely not. Of course, flowering plants are assumed to be
monophyletic, and their common progenitor would also be ancestral to
cps, but many lines of non-cps are interposed.
> What is the "Lucy" of CPs?
There is none.
> How old are they?
A good question. Most cp origins can only be guessed.
The most primitive cp line is possibly Nepenthales (incl.
Droseraceae, Nepenthaceae, Drosophyllaceae, and Dioncophyllaceae).
The order belongs to Caryophyllidae, a subclass that occupies a not
fully understood position within the dicotyledons (it seems to be
quite remote from all the most primitive subclasses as well as from
Rosidae or Asteridae). The oldest fossil representative is the
already mentioned _Aldrovanda_ progenitor. The origins of the family
Droseraceae that may have contained many more genera than nowadays
cannot be located without doubt. _Aldrovanda_ is probably an
originally Eurasian element, but at the early times of its
origination, Eurasia was connected to North America, where the genus
has never been recorded. So it perhaps occupied only the Eastern half
of Laurasia during the Cretaceous. The oldest known (=assumed)
_Dionaea_ ancestor fossils are from the European Tertiary, and the
genus is quite probably much older, so it may have occupied a range
from its recent area of distribution to the east, including parts of
what is now Europe (the Atlantic was much narrower in the Cretaceous,
and the climate was at least for some periods of time warmer than
nowadays). Perhaps _Dionaea_ (the most archaic genus in Droseraceae)
is an early western side line developed from some early _Aldrovanda_
species (_A._ consisted of several species in earlier times).
_Drosera_ appears to be a modern line of Gondwanan origin. This does
not fit the recent preferences of _Aldrovanda_ or _Dionaea_ well, and
it shows that the family must have reached the southern hemisphere
until Early Tertiary (there are Tertiary _Drosera_ pollen fossils
from Africa, Australia, and India). All recent lineages of _Drosera_
do have representatives on the southern hemisphere, and SW Australia
and the Cape region of S Africa are (possibly secondary) centres of
recent diversity.
_Nepenthes_ appears in the fossil record of the Tertiary. The genus
was reported from its recent places of distribution (India,
Indonesia) plus some intriguing finds from the Kerguelen islands in
the S Indian Ocean. These records hint at a likewise Gondwanan origin
of the genus. Fossil pollen from the European Tertiary attributed to
_Nepenthes_ may indicate a formerly more expanded global range of the
genus, but the attribution may be wrong, and the genus did most
probably not originate here (otherwise it could not be explained why
it is missing in Africa, where the following lines are richly
represented). There is no good reason to assume that _Nepenthes_ was
not predominantly E Gondwanan/SE Asian since its earliest beginnings.
_Drosophyllum_ (Drosophyllaceae) occupies a typically relict range in
SW Europe and NW Africa. Its closest recent relatives
(Dioncophyllaceae, Ancistrocladaceae) occur in tropical W Africa, and
the separation of the lines may have been completed by the extension
of the Sahara, in which neither of these plants can survive. The
origins of all three families are obscure, but it can be supposed
that they are all old (perhaps existing since Cretaceous, probably
originated in C Gondwana but quite curiously not represented in S
America).
Cephalotaceae hold a completely surprising, isolated phylogenetical
position (from genetical investigations apparently most closely
related to Cunoniaceae, Elaeocarpaceae, and Oxalidaceae, neither of
which bears any close resemblance to _Cephalotus_, indicating a very
early split from the common ancestor). No old fossils of the genus
are known, and this narrow SW Australian endemic is the greatest cp
enigma of all with respect to its evolution. The attribution to
Saxifragales s. lat. is probably wrong (Saxifragales, even after
inclusion of Hamamelidaceae and Paeoniaceae, do not include the clade
with _Cephalotus_), but a prae-Rosid position is likely.
Sarraceniaceae are (AFAIK) not represented in the fossil record. From
their recent distribution an American origin is quite certain.
Genetical investigations place _Darlingtonia_ at the base of the
family, while almost all morphological and ecological data support
_Heliamphora_ as the most primitive genus. Interestingly, the most
closely related family seems to be Roridulaceae, and both are members
of an extended Ericid clade including Ericales, Theales and
Primulales as the characteristic orders. The disjunction between
Sarraceniaceae and Roridulaceae (together with the huge differences
in morphology) suggest an old age here as well, but the sympetalous
Ericidae appear to be younger than Caryophyllidae and Rosidae, so a
Tertiary origin cannot be excluded although at this time the Atlantic
Ocean must already have been effective as a barrier to dispersal
(which makes the distribution of Sarraceniaceae in America and
Roridulaceae in S Africa more difficult to explain by simple
migration).
All remaining cps (Byblidaceae and Lentibulariaceae, and even the sub-
carnivorous Martyniaceae) belong to Scrophulariales, an Asterid order
that cannot be much older than Palaeocene (Early Tertiary). Both
Lentibulariaceae and Martyniaceae evidently have a tropical
American origin (most genera, subgenera, sections and species,
several of which endemic, are known from C America and N S America).
Several lines of secondary diversification outside America (e.g.
in Africa, tropical Asia, or Australia) are known in _Utricularia_ and
to a much reduced degree in _Pinguicula_ (Europe). Long distance
dispersal (from S America to W Africa and to Australia in
_Utricularia_, from N America to Europe in _Pinguicula_) did probably
occur several times in Lentibulariaceae.
_Byblis_ is apparently the most primitive Scrophularialean cp. It is
restricted to Australia and New Guinea, and its closest relatives are
unknown (it can only generally be placed in Scrophulariales with
some certainty, but the relationships within this order can so far
not be resolved with genetical or phytochemical, nor with
morphological methods). Age and place of origin are unknown but
possibly Byblidaceae are as old as the oldest Scrophulariales and
originally from Australia or SE Asia, not close nor directly ancestral
to Lentibulariaceae or Martyniaceae.
> What period did they come from?
See above.
> Are there any back issues of the newsletter that mention this?
There was a series of papers in CPN by Dr. Degreef that summarized
the knowledge up to that date (early 1990's). In the meanwhile many
new data have been obtained from genetical, phytochemical, and
palaeontological investigations, and somewhat more precise hypotheses
can be formulated. I do intend to write a short review for CPN on this
topic.
> If I've learnt correctly from that recent posting on Chromosome
> counts by Ivan Snyder, ought not the oldest CP to lie with those
> species having the smallest number of chromosomes?
Not exactly. This only applies to polyploid series (e.g. the
representatives of _Pinguicula sect. Pinguicula_ in Europe). Within
such a series polyphyletic speciation (hybridization of two
different lines) can lead to chromosome doubling, so the species with
maximum n in x*2^n (x=chromosome base number, n integer) can only be
of later origin than the parent species. However, hybridization of
two lines with different ploidy can lead to intermediate counts, and
the resulting hybrids are younger than both the line with the lower
count and the line with the higher count (a hybrid between a plant
with 2n=32 and a plant with 2n=16 will have 2n=24, which is lower
than 32 and the hybrid is younger than the parent). Furthermore,
intermediate counts can be caused by different events: 2n=48 can be
caused by chromosome doubling in plants with 2n=24 or by
hybridization between two plants with 2n=32 and 2n=64, respectively.
In the mentioned section, _P. corsica_ and _P. nevadensis_ are the
species with the lowest count (2n=16), the common ancestor may be _P.
villosa_, which has likewise 2n=16 chromosomes.
> What is this lowest number?
2n=6 (in some strains of _Drosera paleacea_). But this does not mean
anything in terms of evolution. Bryastrum (pygmy sundews) is a subgenus
characterized by diffused centromeric chromosomal organization. This
makes chromosome loss, fusion, and fragmentation more likely than in
plants with localized centromeres. While most lineages within _Drosera_
have a base number of x=10, chromosome numbers of 2n= 6, 7,. 8, 10, 12,
14, 17, 18, 20, 28, 32, and 64 (the last two counts are only known from
the also geographically disjunct species _D. pygmaea_) have been found
in Bryastrum alone. The second most diverse group, subgen. Ergaleium
(cormous sundews) likewise displays a great multitude of counts:14, 20,
24, 26, 28, 30, 32, 40, not necessarily indicating any evolutionary
series. Thus unfortunately, chromosome numbers are not suitable for
phylogenetic considerations in Australian _Drosera_, where most of the
recent diversification in the genus has occurred.
The most archaic species of _Drosera_, _D. regia_, has 2n=34.
_Aldrovanda_: 2n=48, _Dionaea_: 2n=32.
All investigated species of _Nepenthes_: 2n=80.
_Drosophyllum_: 2n=12; _Triphyophyllum_: 2n=24, 36.
_Cephalotus_: 2n=20.
_Sarracenia_: 2n=26, _Darlingtonia_: 2n=30, _Heliamphora_: 2n=42
(not correlated to any other trend!); _Roridula_: 2n=12 (possibly
ancestral?).
_Byblis_: 2n=14, 24, 32.
_Pinguicula_: 2n=12 in _P. lusitanica_, which is also possibly the
most primitive species (its closest relatives are all from N America,
and _P. sharpii_ does also have a low chromosome count of 2n=16).
_Utricularia_ is not well surveyed, but the assumedly primitive
species (_U. scandens_, _U. polygaloides_, both belonging to sect.
Oligocista) do have 2n=14 chromosomes, the lowest known count in the
genus, followed by likewise primitive species (_U. uliginosa_, _U.
minutissima_, Oligocista, Australes) with 2n=16 chromosomes. A larger
number of lineages has 2n=18 chromosomes, and most species do have
at least 2n=20.
Kind regards
Jan
This archive was generated by hypermail 2b30 : Tue Jan 02 2001 - 17:35:08 PST