Phylogenetics and demography of the western North American endemic Pacific Laurasian Clade of Isoëtes

The hydrophilic lycopod genus Isoëtes L. has a naturally patchy
distribution, made more extreme due to anthropogenic habitat degradation.
We used a combination of population genetic and multi-locus molecular
phylogenetic approaches to understand the effects of this patchiness on
the evolution and demography of the Pacific Laurasian Clade (PLC) species,
to decipher the relationships among the three PLC species, and to
determine the degree of isolation of the different populations. We
discovered that the populations studied are highly structured and that two
of the species, as currently circumscribed, are not monophyletic. Instead,
our phylogenetic results suggest that there are eight species within the
PLC; of these eight, five appear to have been the result of a rapid
radiation that was followed by a prolonged period of stasis.