Ginkgo

Tom McWilliams mcwillia at msu.edu
Wed Dec 6 02:08:54 EST 2000


Hey guys, I thought the Ginko was considered the first *deciduous* tree?

Parallel veination, like a spread needle;
Wind-borne pollen;
No seed coat, but defintely a seed...

-Tm

Rick Toomey wrote:
> 
> 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


-- 
           *    .             *    '^
           ,..              "  .    *
         ,
             '         Tommy Mac






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