Doctor of Philosophy (PhD)
Phylogenetic relationships and classification of Chrysothamnus, Ericameria, Xylothamia and related genera were investigated. The internal transcribed spacer and 3' external transcribed spacers (ITS and ETS) of the nuclear ribosomal (nr) DNA were analyzed separately and combined employing different optimality criteria. These analyses indicated that the previous classifications and hypotheses of relationships were not monophyletic. Chrysothamnus, Ericameria, Xylothamia, and related genera were placed in separate lineages irrespective of data set and optimality criteria. Chrysothamnus species, as traditionally delimited, were resolved in four, not necessarily closely related lineages affiliated with the Solidagininae. Previous sectional classification of Chrysothamnus based primarily on morphology was not supported by the present molecular data. Ericameria was placed in a clade separate from both Chrysothamnus and Xylothamia. Associated with, but basal to, the Ericameria lineage was a clade composed of Pentachaeta, Rigiopappus, and Tracyina. Prior infrageneric classification of Ericameria was in part consistent with the results of this investigation. Species were placed in three, rather than four, lineages within the genus. The three annual genera and Ericameria represent a lineage separate from the Solidagininae and Hinterhuberinae. Species of Xylothamia were not monophyletic but were placed in at least five separate lineages. Four species were aligned with Gundlachia, while the others were strongly supported in a separate clade. Within that clade, however, the other species were usually in distinct, but unresolved lineages. Xylothamia and its relatives were resolved in a clade distinct from other Solidagininae and merits recognition of their distinctiveness. Both Stenotus and Tonestus were polyphyletic. Type species of both genera were associated with other clades, and the relationship of most of the other species remains unclear. These results suggest a reclassification of these taxa into novel, distinct genera. In general, the results of this study were incongruent with relationships inferred from morphology.
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Roberts, Roland P., "Phylogeny of Ericameria, Chrysothamnus and related genera (Asteraceae : Astereae) based on nuclear ribosomal DNA sequence data" (2002). LSU Doctoral Dissertations. 3881.
Lowell E. Urbatsch