polarizing embryo sac characters, etc. (was Amborellaceae or Nymphaceae first?)
kinman2 at YAHOO.COM
Mon Jan 26 21:53:17 CST 2004
Until we know more about the development of embryo and endosperm in Austrobaileya and especially Trimenia, I don't think we can determine what might be most parsimonious. I'm hoping it will be a relatively simple serial transition:
haploid endosperm (in gymnosperms), to diploid endosperm (in Nymphaeaceae and Illicium), to triploid endosperm (in Amborella and most other angiosperms). But nature is not always so accomodating (e.g., possible reversals of triploid to diploid, or diploid to triploid more than once), so we will just have to wait and see what further evidence shows.
I suspect the putative "pollen with tectum" synapomorphy (proposed to separate Amborella from other extant angiosperms) may not hold up under closer scrutiny. The lack of oil cells in Amborellaceae and Nymphaeaceae could be reversals (losses). I think a possible relationship between Amborellaceae and Trimeniaceae needs particular attention, and to seriously question the holophyly of the ITA "clade" (Austrobaileyales sensu lato). If they are more closely related, the question then becomes whether Amborella slides up the cladogram toward Trimeniaceae, or vice versa.
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