In article ,
Stewart Robert Hinsley writes:
| |
| | From then above cited paper, I. hederacea, I. nil and I. indica are a
| | group of closely related species. (Reading between the lines lumpers may
| | be tempted to place them in a single species.) Again from the cited
| | paper, I. hederacea selfs, I. nil is self-compatible and I. indica
| | self-incompatible.
|
| I am not so much skeptical as completely croggled! Exactly how a
| single species could have variants like that makes me certain that
| I am not using the term "species" in the same way as you (or the
| authors, if you are quoting them) are!
|
| I hope it was obvious that I wasn't quoting them, when I said "reading
| between the line".

What I meant was I wasn't judging whether that was your opinion or
whether you were merely reporting it! You didn't say :-)

| Another paper, which I perhaps should have mentioned, is Shinners,
| Untypification for Ipomoea Nil (L.) Roth, Taxon 14(7): 231-234 (1965).
| The little I can see of this seems to imply that Linnaeus didn't
| distinguish between I. nil and I. hederacea.

The little I know includes the fact that Ipomoea was one of the genera
where Linnaus's view of the species was very different from the modern
one - and even the pre-DNA modern one. It is surprising that there are
so few.

| Self-incompatibility is not always absolute, and may vary among the
| self-incompatibility alleles in a species. There is precedent - Malus
| domestica - for a species containing both self-compatible and
| self-incompatible genotypes. And in general, it does not seem
| implausible that a population of a species could lose
| self-incompatibility with relative ease.
|
| ...
|
| So, while I am not going to argue that they are all a single species -
| I'd have to know more about the group first - I don't think that the
| difference in breeding system is a disproof of the hypothesis. ...

Yes, indeed, but this brings me onto another reason that I regard
so much of modern plant taxonomy as being the modern equivalent of the
mediaeval theologians spending lifetimes analysing how many angels
could dance on the head of a pin.

Even ignoring the question of monophylogeny, the concept of species is
severely flawed even in vertebrates (as Darwin knew), and almost hopeless
for many plants. Most specialists are aware of this, intellectually,
but far too many fail to draw the obvious conclusion that taking
classification into species too seriously leads directly to madness.
The UK classic is, of course, the bramble :-)

By any reasonable traditional definition, plants as different as
I. indica and any of the species we grow as annuals count as different
species. Just as Malus domestica counts as a single (or small number of
species), despite having SOME essentially incompatible varieties. The
simple fact is that species identity is NOT an equivalence relation!
Without learning a lot more, I can't comment about the others.

I wasn't considering JUST the difference in breeding system, incidentally,
as that would have me committing an intellectual faux pas that I have
accused others of :-)


Regards,
Nick Maclaren.