[Taxacom] Usefulness vs. convenience (Protista)
Tony.Rees at csiro.au
Tony.Rees at csiro.au
Sat Dec 18 14:43:51 CST 2010
Well I guess I can see one reason why delineation of a separate kingdom Chromista might have some appeal - it then allows one to bring in the brown multicellular/macro- algae as Chromists even though they are not really protozoa/protists in the "unicellular organism" sense, thereby bringing this "kingdom" more onto a level with the other multicellular "kingdoms" i.e. animals/metazoa, plants, and fungi.; otherwise where do the brown algae live, with the abandonment of a polyphyletic "algae".... still a problem I guess, unless they are pushed back into plants, which no longer seems either useful or convenient? I have seen phylum Heterokontophyta/ stramenopiles/ ochrophyta etc. for these but again, you have to allow this group to include both unicellular and multicellular forms somehow, including some of the biggest "plants" (at least non-animals) of the sea.
Similarly but possibly a bit less intractable, the Rhodophyta, which are not on the green plant line so not viridaeplantae at least, but equally not really protists; finding a treatment which fits well with these and the brown algae seems tricky when some are in/out of kingdom protista/protozoa, but not plants either...
Regards - Tony
From: taxacom-bounces at mailman.nhm.ku.edu [taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Kenneth Kinman [kennethkinman at webtv.net]
Sent: Saturday, 18 December 2010 3:56 PM
To: taxacom at mailman.nhm.ku.edu
Subject: [Taxacom] Usefulness vs. convenience (Protista)
As far as I know, most workers who still use Kingdom Protista are
referring to the traditional broad grouping (with both pigmented and
colourless forms). Chloroplasts have independently invaded colourless
forms several times, so pigmented vs. colourless forms should not be
used to broadly classify protistan taxa at these highest levels.
Cavalier-Smith (1998) divides Protista into two separate Kingdoms
(Protozoa and Chromista), both of which contain colourless and pigmented
forms (which is not a problem per se). However, some workers believe
Chromista is polyphyletic (which would be a huge problem).
My position has always been that whether Kingdom Chromista is
polyphyletic or not, it was still a bad idea, because it unnecessarily
makes his other Kingdom (Protozoa) even more paraphyletic either way.
If Chromista is holophyletic, it basically adds one more exgroup, but
why split Protista if Protozoa is still paraphyletic (there's no
significant advantage gained), And more importantly, if Chromista is
actually polyphyletic, it is not only unnatural, but adds even more
exgroups to Protozoa. It then really makes a huge mess of it.
Either way, it unnecessarily makes the classification more complex
and less stable. As much as I respect Cavalier-Smith's work, this was
his one major mistake, and it seems to have cast a bit of a cloud over
much of the wonderful work he has done on the phylogeny of protists (and
prokaryotes as well). I sincerely hope that he will stop trying to
divide Kingdom Protista into separate Kingdoms, and that his work will
then gain more support. He certainly is not a strict cladist, so why he
wanted to divide Kingdom Protista into separate Kingdoms still puzzles
me. Especially since he otherwise has incredible insight into how to
best subdivide the protists.
Tony Rees wrote:
Ken - I tend to agree (for what it's worth) - you wrote:
Kingdom Protista (as
part of the Five Kingdom classification) has long served as a convenient
paraphyletic group of all eukaryotes except Metazoa, Metaphyta, and
Fungi. Cavalier-Smith has done a fine job of gradually elucidating the
relationships within Kingdom Protista. Unfortunately, he also divided
this perfectly good taxon into separate Kingdoms that proved to be
either wrong or controversial (which has puzzled me since he does
recognize some paraphyletic taxa). </snip>
Yes - now when someone talks about Protista, do they mean:
- colourless unicellular organisms (without the pigmented ones i.e.
"microalgae" or phytoflagellates etc.) i.e. ~= protozoa
- all unicellular organisms, colourless and pigmented i.e. Protista
sens. lat., pre C-S "Chromista" split
- same less the heterokont algae and related colourless forms i.e
Protista less Chromista Mk 1
- same less the heterokont algae and related colourless forms, also
rhizaria and alveolates i.e. Protista less enlarged Chromista (2010
all very confusing (especially to casual readers) and also unstable
between versions and between different authors/usages...
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