Phylum Pteridophyta (classification modified)

[Curtis Clark]

on 2005-03-14 08:01 Ken Kinman wrote:
> I just hope the
> strict cladists haven't insisted on formally naming the
> Hepaticopsida-Bryopsida clade, because it doesn't seem absolutely
> necessary and certainly isn't a done deal.

I agree with the latter; mosses seems to share too many apomorphies with
tracheophytes to make that cut-and-dried.

> ******************************************************* Sorry Curtis,
> but your latest suggestions won't work.  Combining Horneophytopsida,
> Aglaophyton, and Rhyniopsida into a single plesion would just make
> that plesion paraphyletic (which I'm sure you don't want).

Plesions are *supposed* to be paraphyletic--that's the whole point. IMO
basal fossil complexes such as that are notoriously difficult to sort
out, and a plesion preserves the knowledge gaps better than either a
formal paraphyletic group or a bunch of poorly-supported formal clades.

> Furthermore, Phylum Pinophyta is
> paraphyletic with respect Phylum Magnoliophyta, so you would also
> have to raise all the Pinophyte classes to phylum level.

Yeah, I noticed that after I hit the send button. But in fact they were
raised to phylum level in general botany texts quite a while ago, and I
seem to remember them being co-equal classes in Phylum Tracheophyta in
Dittmer's text from the 1960s.

Ironically, recent molecular evidence suggests that the gymnosperms
might be a clade.

> Anyway, I am quite happy with the above
> classification, although considering your suggestion, I just might
> slide Progymnospermopsida back into the base of Phylum Pinophyta (as
> I did in 1994).  It depends on which of the two options is supported
> by the most clear-cut synapomorphy (and if that is congruent with
> your "less egregious" criterion, all the better).

Putting the progymnosperms in a taxon with ferns is like including all
the synapsids *except* the pelycosaurs and anything basal to them in the
Mammalia, but leaving the pelycosaurs in the Reptilia. I supposed it all
depends on what features you think best show "divergence", but to me
that's the true measure of the arbitrariness of paraphyletic groups.

--
Curtis Clark                  http://www.csupomona.edu/~jcclark/
Web Coordinator, Cal Poly Pomona                 +1 909 979 6371
Professor, Biological Sciences                   +1 909 869 4062