Amborellaceae or Nymphaeaceae first??
peter.stevens at MOBOT.ORG
Tue Jan 13 12:30:10 CST 2004
> The general consensus presently has
>Amborellaceae as the most primitive clade of extant
>flowering plants, and then Nymphaeaceae as the next
>clade to split off (and that's how I coded it in my
>angiosperm classification presented here, May 2003).
>However, Amborellaceae's claim to being the first is
>apparently being disputed in at least two recent
> (1) Goremykin VV, Hirsch-Ernst KI, Wolfl S, and
>Hellwig FH. 2003. Analysis of the Amborella
>trichopoda chloroplast genome sequence suggests that
>Amborella is not a basal angiosperm. Mol. Biol.
There is a paper in AJB number 12 this year that tends to support the
basal position of Amb. Doubtless things will have cleared up in a
couple of years or so (I hope...).
> (2) Friedman WE, and Williams JH. 2003.
>Modularity of the angiosperm female gametophyte and
>its bearing on the early evolution of endosperm in
>flowering plants. Evolution Int J Org Evolution,
> The first paper listed above would not concern me
>too much in isolation, but the paper by Friedman and
>Williams also seems to dispute the present consensus
>phylogeny since Amborella apparently has female
>gametophytes of the more derived eight-nucleate
>(double module) type. Of course, I guess it's
>possible the eight-nucleate type evolved more than
>once. Anyway, Nymphaeaceae is one of the few
>angiosperm families with the four-nucleate (single
>module) type. Any comments?
If you read the numeorus other excellent papers of Friedman et al.
you will find that Austrobaileyales studied also have the same kind
of embryo sac as Nymphaeales, so that makes any simple optimisation
of the 8-nucleate embryo sac on the tree ambiguous. Also, even
within Amborella, the actual behavior of the nuclei may differ from
that in 8-nucleate sacs of other angiosperms. One thing that
Friedman et al. are trying to do is to beak down our typologies such
as 8- versus 4-nucleate sacs, nuclear versus cellular endosperm, etc.
In haste, have to write a lecture.
> ------- Cheers,
> Ken Kinman
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