TAYLOR, W. CARL* AND SARA B. HOOT. Botany Department, Milwaukee Public Museum, Milwaukee, WI 53233 and Department of Biological Sciences, University of Wisconsin, Milwaukee, WI 53201. - Evolutionary relationships and biogeography of Isoetesbased on nucleotide sequences.
Nucleotide sequences from the internal transcribed spacer (ITS) region
of nuclear ribosomal DNA and the atpB-rbcL spacer region
of the chloroplast genome were used to resolve species relationships
of Isoetes from a worldwide perspective. Basic diploid species
from North and Central America, Europe, Africa, Asia, and Australasia
were included. A well-supported, putatively Gondwanian clade
consisted of I. stellenbossiensis and I. capensis of
South Africa, I. coromandelina of India, and I.
panamensis of Costa Rica. Results demonstrated a close,
well-supported relationship of the Asian taxa (I. kirkii of New
Zealand, I. drummondii of Australia, and I.
taiwanensis). North American species of Isoetes are not
monophyletic. Two western North American species (I. nuttallii
and I. orcuttii) were found in a well-supported clade
consisting of European and African species. The remaining, weakly
resolved North American clade of 15 species included I.
mexicana and I. storkii of Costa Rica. The two species
from Costa Rica (I. panamensis and I. storkii) and two
species from Spain (I. setacea and I. velata) were not
closely related, appearing in widely divergent clades. The resulting
phylogeny and the number of substitutions and indels supporting the
branches suggest that some clades are of relatively ancient origin,
whereas others (the weakly resolved North American clade) are much
Key words: biogeography, evolutionary relationships, Isoetes, nucleotide sequences