BAIRD, GARY I. Department of Botany and Range Science, Brigham Young University, Provo, UT 84602. - A phylogenetic assessment of Chrysothamnus Nutt. (Asteraceae, Astereae).
The genus Chrysothamnus Nutt. is comprised of a group of
asteraceous shrubs distributed throughout the western United States
but with a center of diversity on the Colorado Plateau. The most
well-known, widely distributed and studied species is C.
nauseosus (Pall.) Britton. This singular taxon tends to dominate
most informal concepts of the genus as a whole. Recent phylogenetic
studies of the tribe Astereae, using cpDNA restriction site data, have
placed C. nauseosus as either sister to or within the genus
Ericameria Nutt. This is a position long supported by
morphological and chemical analyses and as a natural consequence has
precipitated the transfer of C. nauseosus into
Ericameria. None of the other species of Chrysothamnus
have been included in these recent phylogenetic studies, yet there is
morphological and chemical data to suggest that at least C.
viscidiflorus (Hook.) Nutt. and possibly some of the other core
Chrysothamnus species are not closely related to
Ericameria but are phylogenetically allied to Petradoria
Greene and its sister taxa within the subtribe Solidagininae. This
apparent phylogenetic contradiction within Chrysothamnus would
suggest that the genus is polyphyletic, as generally construed. The
purpose of the current study is to test the monophyletic nature of
Chrysothamnus and resolve its putative phylogenetic
relationships using DNA sequence data, in addition to morphological
data.
Key words: Chrysothamnus, DNA, Ericameria, Petradoria, phylogeny