[Taxacom] Angiosperm origins: Darwin's "abominable" mystery

[Michael Heads]

Hi Jeremy,
 
The details of double fertilisation are indeed highly variable. Double fertilisation in angiosperms is sometimes specified as ‘double fertilisaton leading to triploid endosperm’, but diploid endosperm is formed in Nuphar by double fertilisation. Double fertilisation events similar to those in Ephedra have also been reported for Thuja and Abies, and events in cycads and Ginkgo are also consistent with double fertilisation. Friedman & Floyd (Evolution, 2001) even suggested double fertilisation may be a synapomorphy for all extant seed plants. 
 
Michael

Wellington, New Zealand.

My papers on biogeography are at: http://tiny.cc/RiUE0

--- On Sun, 21/3/10, Jeremy Bruhl <jbruhl at une.edu.au> wrote:


From: Jeremy Bruhl <jbruhl at une.edu.au>
Subject: Re: [Taxacom] Angiosperm origins: Darwin's "abominable" mystery
To: taxacom at mailman.nhm.ku.edu
Received: Sunday, 21 March, 2010, 2:49 AM


Double fertilization of angiosperms and gnetophytes share the name not the
ontogeny; they are different.

e.g. see Ephedra shows double fertilization of a sort, which is
analogous or, in my opinion, homologous to that in
angiosperms (Krassilov, 1997)
http://www.springerlink.com/content/k18165643020v321/fulltext.pdf

Cheers
Jeremy

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Michael Heads
Sent: Saturday, 20 March 2010 2:52 PM
To: Thomas Lammers
Cc: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Angiosperm origins: Darwin's "abominable" mystery


Thomas,
 
I think that's a good characterisation, using population diversity.
Also, the angiosperm characters may have evolved before the angiosperm
clade. This would explain why there is so much incongruence, with
classic angiosperm characters such as double fertilisation occurring in some
gymnosperms and not in all angiosperms.
 
Michael Heads 

Wellington, New Zealand.

My papers on biogeography are at: http://tiny.cc/RiUE0

--- On Sat, 20/3/10, Thomas Lammers <lammers at uwosh.edu> wrote:


From: Thomas Lammers <lammers at uwosh.edu>
Subject: Re: [Taxacom] Angiosperm origins: Darwin's "abominable" mystery
To: "Curtis Clark" <jcclark-lists at earthlink.net>
Cc: taxacom at mailman.nhm.ku.edu
Received: Saturday, 20 March, 2010, 3:11 PM


----- Original Message -----
From: Curtis Clark <jcclark-lists at earthlink.net>

> Axelrod introduced me to the idea of Triassic angiosperms; his contention
was that, because they evolved in the uplands, we'd be unlikely to see
fossils.<

I try to imagine what it would be like if we could travel back to study in
the field the population to which the angiosperms of today trace their
origin.  I don't imagine we would see anything that, in the context of the
flora of that time, would stand out as all that different.  The
population-biology view of evolution suggests that the characters that today
are hallmarks of a well-distinguished class or phylum would likely have been
mere intrapopulational variation at the earliest points in time. "Oh, look! 
In some of the plants in this population, the second sperm nucleus fuses
with the polar nuclei!  What an odd little aberration!"  

Furthermore, even as some of these traits stabilized in species, it still
may have been awhile before "anything came of it."  Just as the mammals
"hung out" for quite a long while in the Mesozoic before getting their
chance to proliferate, so too might angiosperms have piddled around, cooling
their heels, for millions of years before opportunity came knocking.  We no
doubt have found and named fossils that, if we could study them as living
entities, we would call angiosperms.

Thomas G. Lammers, Ph.D.

Associate Professor and Curator of the Herbarium
Department of Biology and Microbiology
University of Wisconsin Oshkosh

http://www.uwosh.edu/departments/biology/Lammers.htm
http://www.kewbooks.com/asps/ShowDetails.asp?id=615



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