Names, ranks, and monophyletic groups

Torsten Eriksson Torsten.Eriksson at BOTAN.SU.SE
Fri Mar 17 14:34:03 CST 1995

Happily following the first debate on this list since I joined almost ayear
ago (!) I have the following comments:

There are two or several issues here which are mixed.

1. The problem of giving a unique name to the basic (or fundamental) unit,
i.e. what most people think about as species. Let's call it species for the
sake of argument, and think of it as a group of organisms in which all are
more closely related to each other than to any other organism (an exclusive
group, cf. de Queiroz, K., and M. J. Donoghue. 1988. Phylogenetic
systematics and the species problem. Cladistics. 4: 317-338).
   Some of you have mentioned that there is a problem with names if they
are not "names" but numbers: in recognition, spelling etc. Today, however,
I don't think that there is any problem in having a "NameBank" which could
assign unique identifiers for any species even on an automated basis. Any
"palustris", "linnaeana", or "hugh" for that matter would have a unique
identifier attached to it maybe like sequences have in GenBank. The
argument here is that this is hardly difficult. It is not even very
problematic. It is a matter of funding.

2. The second problem is one of grouping and I agree with both Curtis Clark
in that grouping is a major part of Systematics, and with David Wright that
the problem here is RANKS!
   A very interesting suggestion on this topic was made by de Queiroz and
Gauthier [for example in TREE. 9: 27-31 (1994). "Toward a phylogenetic
system of biological nomenclature"]. They suggest that ranks should be
abandoned, and I agree, since ranks obviously have NO meaning unless they
are also monophyletic groups.
   De Queiroz and Gauthier also suggest that a name, any name, instead
could be assigned to a monophyletic group. This monophyletic group would be
defined as all the decendants of the closest ancestor of TWO specified
species (as used above). I find this suggestion to be very interesting
because it would be a way out of the present mess of ranking into a more
natural system. In naming a species within its hierarchy, for example, one
could use a "phrase", naming the (unique) species, and one or several of
the monophyletic groups it belongs to, in order of inclusivity.
   For example, let's assume a unique species name vesca(XLS8976P) is a
species which is included in a monophyletic group "Fragaria" which is
included in a monophyletic group "Rosoideae", one could name it:
Rosoideae Fragaria vesca(XLS8976P)  ...or...
Rosoideae vesca(XLS8976P) ...or...
Fragaria vesca(XLS8976P) ...or...
   To use just the binary "Fragaria vesca" would not be exact but
unproblematical within small monophyletic groups, meaning the species
"vesca" within the more inclusive monophyletic group "Fragaria".

When it comes to types, I think that they are necessary for species (as
used above) for practical purposes, but groups of species should be
monophyletic groups - and a monophyletic group can never have ONE type and
still have unequivocal borders. To have TWO "type species" as suggested by
de Queiroz and Gauthier would solve that problem.

Torsten Eriksson
Botaniska institutionen               email: torsten.eriksson at
Stockholms universitet                                  tel: +46 8 163868
106 91 Stockholm                                        fax: +46 8 162577

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