Phylogenetic Significance of Chloroplast DNA Restriction Site Variation in the Ipomopsis aggregata complex and related species (Polemoniaceae)

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Systematic Botany



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The Ipmopsis aggregata complex comprises diploid, perennial, montane herbs, distributed across western North America. We used chloroplast DNA (cpDNA) restriction site variation to examine phylogenetic relationships among the three species in the complex, l. aggregate, I. arizonica and l. tenuituba, and several related species. Twehnty-one restriction site mutations and four length mutations were used to reconstruct a phylogenetic tree by cladistic methods. With a few exceptions, patterns of cpDNA variation within l. aggregata were consistent with current taxonomy and reflected the geographic distributions of subspecies and populations. However, spDNA-based relationships among species were not congruent with a pre-1992 taxonomy of the group. Ipomopsis ternatuba did not form, a distinct clade; two popultaions of this species had the same "primitive" cpDNA as l. arizaonica and l. rubra, whereas two other populations emerged on branches within l. aggregata, and one population (of l. tenuituba subsp. macropsiphon) shared mutations with l. thurberi. It is noth clear whether this pattern is the result of cpDNA transfer during periods of hybridization or the "tenuituba" morphology has arisen independently more than once. Ipomopsis tenuituba subsp. macrosiphon has subsequently been segregated as a species. The level of sequence divergence among species was similar in magnitude to that among populations within each species, consistent with patterns of recent divergence and subsequent hybridzation among the three species in the complex. In addition, relationships based on cpDNA variation reflected taxonomy and geographic distribution more congruently than did allozymes. THe results from this study suggest that evolution of the l. aggregata complex has involved cases of chloroplast DNA transfer between taxa, convergent evolution for certain floral characters, or both

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