need suggestions

[Curtis Clark]

At 02:43 PM 1/4/96 -0500, 06jlsmith at BSUVC.BSU.EDU wrote:
>African violets belong to a genus with a relative small geographical
>range (parts of Tanzania and Kenya).  Although 20 species have been
>described, it is now becoming apparent that most of these "species"
>were described from small populations of individuals.  When brought
>into cultivation, almost every species will cross easily with another
>and give fertile offspring.  There does not appear to be any genetic
>barriers between the species.
>
>Question - in other plant groups, what guidelines have been used to
>define a "species" in situations like this?  Should a species be one
>of the local populations that can be identified by morphological
>characteristics, or should the ease with which the plants hybridize
>be taken into account?

In Encelia of the Asteraceae, species hybridize freely in cultivation and
with some frequency in the wild, but, outside of these wild hybrids, the
species maintain morphological distinctiveness, and phenotypic and DNA
character sets are generally consistent with a divergent phylogeny.  There
are other similar examples (e.g., Quercus subgenus Quercus), but this is the
one I am most familiar with.  To me the question would be, are the
populations distinctive in the wild, and does the pattern of distribution of
their differences fit processes of divergent evolution (rather than
reticulation)?  If so, they are species.

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Curtis Clark        http://www.sci.csupomona.edu/biology/clark/clark.htm
Biological Sciences Department                     Voice: (909) 869-4062
California State Polytechnic University, Pomona    FAX:   (909) 869-4396
Pomona CA 91768-4032                               jcclark at csupomona.edu
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