Fwd: Re: rankless nomenclature

[Philip Cantino]

Jean-Michel Maes asked:

>By the way, I do not understand "rankless", my english is really deficient.
>Is that a system without rank, without families, genera, etc... I understand
>phylogeny as a system which make groups (no important how you name the
>groups) then there is a hierarchy, Isn't so ?
>

What "rankless" means in phylogenetic nomenclature is that one is not
required to give a taxon a rank in order to name it, and if one
decides to give it a rank (which is permitted), the rank has no
bearing on the spelling or application of the name.  The decoupling
of the rank from the name eliminates a major source of nomenclatural
instability in the rank-based system--name changes due to shifts in
rank.

In rank-based nomenclature, priority is applied within rank (at least
at and below the family level), so if a taxon is moved to a different
rank, its name must change.  In phylogenetic nomenclature, priority
is independent of rank.  Thus, shifting the rank at which a clade is
recognized does not change the priority of names.  If a name has
priority for a particular clade at the family rank, it also has
priority at all other ranks if ranks are used.

One implication of this is that the endings of names have no
significance in phylogenetic nomenclature.  For example, in the
rank-based system, a plant taxon called Ajugoideae is necessarily a
subfamily but may or may not be monophyletic.  In phylogenetic
nomenclature, a plant taxon called Ajugoideae is necessarily a clade
but may or may not be ranked as a subfamily (or ranked at all).

Phylogenetic names fall into a hierarchy because the evolutionary
process produces a natural hierarchy of groups.  However, the
position that a taxon holds within the hierarchy does not affect its
name in phylogenetic nomenclature, whereas it does in the rank-based
system.  Thus, phylogenetic nomenclature separates nomenclature from
classification to a greater extent than the rank-based system does.

Phil



Philip D. Cantino
Professor and Chair
Department of Environmental and Plant Biology
Ohio University
Athens, OH 45701-2979
U.S.A.

Phone: (740) 593-1128; 593-1126
Fax: (740) 593-1130
e-mail: cantino at ohio.edu