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Abstract

The most recent assessments of phylogenetic relationships and diversification in the flowering plant family Polemoniaceae have relied on nuclear ribosomal and chloroplast DNA sequences. We employed the mitochondrial nad1b intron, located within the second transcription unit of the first subunit of NADH dehydrogenase, for phylogenetic inference. Maximum parsimony analysis of these data provided evidence that Polemoniaceae are more closely related to families Fouquieriaceae, Diapensiaceae, Styracaceae, and Primulaceae than to families of the Solananae, where it has been classified. Fouquieriaceae are inferred to be the sister group of Polemoniaceae; however, when indels are treated as additional characters and given twice the weight of a nucleotide substitution the sister group of Polemoniaceae is a clade that includes Fouquieriaceae, Diapensiaceae, and Primulaceae. Mitochondrial DNA sequences also provided support for an early diversification of Polemoniaceae involving three lineages: the Acanthogilia lineage, the Cobaea-Cantua-Bonplandia lineage, and a lineage including the remaining sampled genera of the family. These results are highly consistent with phylogenetic estimates based on chloroplast and nuclear gene sequences. However, because the exact branch order is not known with confidence for these three lineages, nor are the closest relatives to Polemoniaceae, assessments of homology in morphological characters remains tenuous. For example, both Fouquieriaceae and Acanthogilia possess primary leaves that become persistent spines. It was shown that, in spite of the morphological similarity, spiny primary leaves in Fouquieriaceae and Polemoniaceae are not homologous.

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© 1998 J. Mark Porter, Leigh A. Johnson

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