[Taxacom] Phylogenetic Classification?

[Boggan, John]

Maybe this has already come up but I don't have the time or patience to
wade through all the discussion in the archives.  How are paraphyletic
species to be treated in strictly cladistic classifications?  I don't
know about animals, but in plants paraphyletic species are probably
quite common, i.e., one or more morphologically distinct and
reproductively isolated species have been derived from a common and
widespread ancestral species that still exists.  Recognizing those
derived species makes the ancestral species paraphyletic, but it is
still a species (or is it?) in that it consists of interbreeding
populations that are united by gene flow while reproductively isolated
from their relatives (including the descendant species).  Should the
derivative species be synonymized under the ancestral species?  And if
not, what are the phylogenetic implications of the subsequent history of
these two taxa, one monophyletic but the other not?

 

Most molecular phylogenies will not reveal this problem (or at best only
hint at it) because they sample only one individual of each species.
But taking the problem to a reasonable extreme, it's theoretically
possible for a single founding individual of a species, landing on an
island, to undergo an evolutionary radiation and give rise to numerous
new genera and species even while the ancestral species still exists on
the mainland, remaining more or less unchanged.  In practice, extinction
of populations and entire species probably saves us from this problem.
But if it could be shown that the founding individual (and thus all its
descendants) was more closely related to one population of the ancestral
species than another, the classification of that group could get awfully
messy...

 

John Boggan

Type Register Project

United States National Herbarium

Dept. of Botany, MRC 166

National Museum of Natural History

Smithsonian Institution

P.O. Box 37012

Washington, DC 20013-7012

 

Email: Bogganj at si.edu

Phone: (202) 633-0895

FAX: (202) 786-2563

Department website: http://www.nmnh.si.edu/botany

Type Register website: http://ravenel.si.edu/botany/types