Ginkgo

Rick Toomey toomey at museum.state.il.us
Tue Dec 5 18:49:44 EST 2000


Hello, 

CorK wrote:
> 
> 
> Fossils and Phenology in the Evolution of Ginkgo biloba,
> Rothwell,Holt, Ohio University
> Cladistics of the Spermatophyta, Brittonia, Loconte, Stevenson
> A reevaluation of seed plant phylogeny, Ann Missouri Bot Gard
> Lignophyte phylogeny and the evolution of spermatophytes, a numerical
> cladistic analysis, Syst Bot
> 
> CorK
> The Ginkgo Pages
> http://www.xs4all.nl/~kwanten
> 

   Thank you for the references (although more complete citations to 
make them easier to find would have been useful).  I have
only been able to evaluate two of the four references that 
you cite.  However, neither of them provide support 
for your contention that ginkgos might be the first 
tree on earth.  

   The two that I can evaluate are as follows  (references
including abstracts):

Authors
  Nixon KC.  Crepet WL.  Stevenson D.  Friis EM.
Title
  A REEVALUATION OF SEED PLANT
  PHYLOGENY
Source
  Annals of the Missouri Botanical Garden.  81(3):484-533, 1994.
ISSN
  0026-6493
Abstract
  Seed plant phylogeny is
  evaluated using a data set of 46 terminals (taxa) and 103
morphological and
  anatomical characters. Cladistic analyses using the criterion of
parsimony
  were performed on the complete data set as well as on subsets of the
data,
  e.g., excluding fossils and/or combining various complex taxa into
single
  terminals. The results support the placement of the cycads as the
sister
  group of a monophyletic group that includes several fossil
  ''seed ferns'' as well as extant Ginkgo, conifers,
  gnetopsids, and angiosperms. When fossils were included, Bennettitales
  (cycadeoids) were part of an ''anthophyte'' clade that included
gnetopsids
  and angiosperms. Pentoxylon was a sister taxon to the core anthophyte
clade,
  in some, but not all, of the most parsimonious trees. Caytonia was not
found
  to be closely associated with the anthophyte clade, but instead was
often
  associated as a sister taxon of the glossopterids, and these two taxa
were
  consistently outside of the Ginkgo-conifer-anthophyte clade. In all
most
  parsimonious trees for all analyses, Ephedra was to the outside of a
clade
  that included all angiosperm taxa, Gnetum, and Welwitschia, thus
rendering
  the traditional gnetopsid clade paraphyletic. New information is
provided on
  the morphology of Caytonia and some previous interpretations of
homology of
  the caytonian ''cupule'' are rejected. The effects of sampling,
  compartmentalization, and polymorphism are explored in these data,
showing
  how different results may be obtained when polymorphic or ''summary''
  terminals are used. The need for more work on gnetopsids and fossil
taxa is
  suggested. [References: 234]

and 

Authors
  Rothwell GW.  Serbet R.
Title
  LIGNOPHYTE PHYLOGENY AND THE EVOLUTION OF SPERMATOPHYTES - A
  NUMERICAL CLADISTIC ANALYSIS
Source
  Systematic Botany.  19(3):443-482, 1994 Jul-Sep.
ISSN
  0363-6445
Abstract
  Phylogenetic relationships of 27 taxa of extant and extinct
lignophytes were
  assessed in a numerical cladistic analysis using 65 characters. The
analysis
  yielded 12 most parsimonious trees, where fossil taxa were found to
play a
  crucial role in the reconstruction of spermatophyte
  phylogeny. The results supported hypotheses of monophylesis
  for spermatophytes, archaeopteridalean progymnosperms, medullosan
  seed ferns, cordaiteans, anthophytes, and gnetophytes.
  Progymnosperms, seed ferns s.l., and hydrasperman
  seed ferns were found to be paraphyletic. A large clade that
  previously has been referred to as ''platysperms'' or ''saccate
platysperms''
  occurs in our results, but it is not characterized by either of these
  features. The results reflect a hypothesized trend from large
dissected
  leaves (the ''cycadophytic'' growth habit) to small leaves and
aggregated
  sporophylls (the ''coniferophytic'' growth habit) in several groups,
and
  coniferophytes (including cordaites, conifers plus taxads, and
ginkgos) were
  found to be polyphyletic. Surprisingly, inclusion of the Late
Pennsylvanian
  voltzialean conifer Emporia renders monophylesis for conifers
(including
  taxads) less parsimonious than polyphylesis under most sets of
assumptions.
  Extinct taxa provided data to clarify the order of character
originations in
  the evolution of spermatophytes. Their inclusion in the analysis also
helped
  clarify homologies among ovule enclosing structures that have been
termed
  ''cupules.'' [References: 141]


    These two references (although very good studies) are not capable of 
actually providing evidence on whether ginkgos are the first tree
for two different reasons.  

     First, since they only deal with seed plants, they fail 
to address whether any non-seed-bearing trees exist (the 
answer is yes).  So, even if ginkgos were the most primitive 
seed plant, that would not necessarily make them the earliest 
tree.  To answer the question of whether ginkgos are the 
most primitive trees, you must look at a phylogenetic analysis
that addresses all vascular plants (not just seed plants).
One recent such analysis is Doyle (1998).  It finds scale 
trees (Lycopsids) to be more primitive that gingkos.  
Sphenopsids and ferns are also more primitive.  
Within seed plants a variety of Paleozoic seed ferns 
as well as Cordaitales may also be more primitive than
ginkgos. Each of these groups also has arborescent 
forms that pre-date ginkgos (so the fossil record fails
to support the ginkgos as earliest tree scenario).
The Nixon and others paper you cite even indicates 
several arborescent fossil taxa are potentially more
primitive than ginkgos.

   The second reason these references are not actually
able to provide the data to support your statement 
is more subtle.  Both of these are phylgenetic studies
that provide information on the relationships of 
the groups.  They can indicate how primitive 
the ginkgo group is; however, they do not indicate
that the earliest ginkgos are trees.  Most of the
taxa have a variety of habits, so tree is not 
necessarily the form in which they first show up.

   As I noted in the first reason, the fossil record
shows a variety of trees that are earlier than 
the earliest ginkgo.  

   I noted I have only been able to look at two of the references; 
however, from the title, Cladistics of the Spermatophyta,
appears to suffer from the same problems as the two 
I have discussed above in being able to provide evidence 
on the claim at hand.  Perhaps you can enlighten us with 
better info on that one.


Reference cited (in addition to the ones cited by Cork)

Doyle JA, 1998, Phylogeny of vascular plants, Annual 
   Review of Ecology and Systematics. 29: 567-599.


Rick Toomey
Illinois State Museum
toomey at museum.state.il.us


> >
> >Hello,
> >
> >CorK wrote:
> >>
> >> On 4 Dec 2000 21:39:40 GMT, una at mercury.cis.yale.edu (Una Smith)
> >> wrote:
> >>
> >> >
> >> >kwantenzap at xs4all.nl (CorK) writes:
> >> >
> >> >>It might well be the first tree on earth, you're not well informed.
> >> >
> >> >It is certainly not the first tree on earth.  CorK, I suggest you go
> >> >*read a paleobotany textbook*;  several good ones have already been
> >> >cited in this thread.
> >>
> >> I have.
> >
> >CorK, since you indicate that you have read a paleobotany text,
> >perhaps you could tell us which one supports your claim that
> >the ginkgo "might well be the first tree on earth."  As a
> >paleontologist,
> >I would definitely support Una's statement that it is certainly
> >not the first tree on earth.  In fact, it is not even close.
> >Trees predate the ginkgo line (let alone the genus Ginkgo), by something
> >like 50 million years.
> >
> >
> >Rick Toomey
> >Illinois State Museum
> >toomey at museum.state.il.us






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