Orthophyletic? was Re: Tree numbers

[Gary Rosenberg]

I hadn't realized that the term "orthophyletic" was not used outside malacology. It appears on page three of  <www.cabi-publishing.org/Bookshop/ReadingRoom/0851993184/0851993184Ch1.pdf>. I think it was coined by Gerhard Haszprunar in the 1980s. An orthophyletic group is a stem group, i.e., a group that is paraphyletic because a single clade (the crown group), has been excluded.

The point of the calculation is that the number of monophyletic groups is proportional to n, whereas the number of paraphyletic groups is proportional to n squared. This is basically an argument against recognizing paraphyletic groups. Say we had a tree of life for a million species (the true tree). Ignoring infraspecific groups, the maximum number of nameable monophyletic groups would be about 2 million (including the million species) whereas allowing paraphyletic groups increases the number of nameable groups to about a trillion.

This is not to say that I'm entirely opposed to paraphyletic groups. I'm sympathetic to the paleontological argument that it wasn't paraphyletic at the time it was alive, and I also believe that a species can be paraphyletic.

Gary Rosenberg

>>> "Stephen C. Carlson" <scarlson at mindspring.com> 05/30/03 03:03PM >>>
Gary Rosenberg <rosenberg at ACNATSCI.ORG> wrote:
>Also, the number of monophyletic groups in a given dichotomous tree of n =
>taxa is 2n-1 and the number of orthophyletic groups is (n-1)(n-2).

I'd never encountered the term "orthophyletic" before.  What does it mean?  Non-polyphyletic (i.e. either monophyletic or paraphyletic)?

Stephen Carlson