polarizing embryo sac characters, etc. (was Amborel laceae or Nymphaceae first?)

Richard.Zander at MOBOT.ORG Richard.Zander at MOBOT.ORG
Mon Jan 26 10:45:57 CST 2004


Isn't reduction clearly defensible only when evolutionary elaboration of
identical elements is really, really improbable. I think we'd have to know
more about the nucleate condition, including associated characters that are
probably not coadapted.

______________________
Richard H. Zander
Bryology Group
Missouri Botanical Garden
PO Box 299
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Fax: 314-577-9595
Websites
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-----Original Message-----
From: STEPHEN MANNING [mailto:SDMANNING at ASUB.EDU]
Sent: Monday, January 26, 2004 9:27 AM
To: TAXACOM at LISTSERV.NHM.KU.EDU
Subject: [TAXACOM] polarizing embryo sac characters, etc. (was
Amborellaceae or Nymphaceae first?)


At 09:23 PM 1/25/04 -0600, Ken Kinman wrote:
>Dear All,
>       The paper by Zanis et al., 2002 (in PNAS) showed some good support
> for Amborella as sister group to the rest of angiosperms, BUT I am still
> not convinced.   In fact, I wouldn't be particularly surprised if
> Nymphaeaceae sensu lato (incl. Cabombaceae) splits off first, followed by
> Illiciaceae sensu lato (with two genera known to be "4-nucleate"), and
> then followed by Trimenia and Amborella (which show some interesting
> similarities), these latter two perhaps even clading together.

This gives me an excuse to mention something I thought of earlier but
didn't post; if the general trend in female gametophyte evolution is
reduction, wouldn't it be more parsimonious to treat the "4-nucleate"
condition as more derived than an "8-nucleate" one?

Sort of an analogy to a general proposition that RNA may be more primitive
than DNA because it only takes one step each way to get to DNA or protein
rather than the two steps it takes to get from DNA to protein?

>  I would almost anticipate some kind of transitional 8-nucleate status in
> Trimenia similar to that in Amborella, but we will just have to wait and
> see.  It should also be interesting to see where Austrobaileya might fall
> into this possible transition.  Anyway, treating "Austrobaileyales" as a
> single OTU (the ITA "clade") at this point is probably ill advised, as it
> could be paraphyletic (or even polyphyletic if Amborella and Trimenia are
> more closely related).  Just too little information to be sure at the
> present time.
>                    ------ Cheers,
>                            Ken Kinman

Stephen D. Manning, Ph.D.
Professor of Biology
Mathematics and Science Division
Arkansas State University - Beebe
P. O. Box 1000
Beebe, Arkansas 72012-1000
USA
Tel: 501-882-7162




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