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Elucidating Deep-Level Phylogenetic Relationships in Saxifragaceae Using Sequences for Six Chloroplastic and Nuclear DNA Regions

Douglas E. Soltis, Robert K. Kuzoff, Mark E. Mort, Michael Zanis, Mark Fishbein, Larry Hufford, Jason Koontz and Mary K. Arroyo
Annals of the Missouri Botanical Garden
Vol. 88, No. 4 (Autumn, 2001), pp. 669-693
DOI: 10.2307/3298639
Stable URL: http://www.jstor.org/stable/3298639
Page Count: 25
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Elucidating Deep-Level Phylogenetic Relationships in Saxifragaceae Using Sequences for Six Chloroplastic and Nuclear DNA Regions
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Abstract

To elucidate relationships at deep levels within Saxifragaceae we analyzed phylogenetically a data set of sequences for six DNA regions, four representing the chloroplast genome (rbcL, matK, trnL-trnF, psbA-trnH) and two from the nuclear genome (ITS and expansion segments of the 26S rDNA). A total of 6676 bp was aligned per taxon, 4559 bp and 1878 bp from the chloroplast and nuclear genomes, respectively. Chloroplast and nuclear trees agreed closely, prompting analysis of a combined, six-gene data set. Application of both parsimony and maximum likelihood methods yielded similar topologies. The use of different ITS alignments and the exclusion of hard-to-align ITS regions had little impact on either the final nuclear-based topology, or the shortest trees from the analysis of six genes. The affinities of two monotypic genera (Saxifragella and Saxifragodes) endemic to Tierra del Fuego were elucidated. Saxifragella is an early branching member of the North Temperate genus Saxifraga s. str.; Saxifragodes is sister to Cascadia, a genus endemic to Oregon and Washington. Long-distance dispersal from east Asia or western North America to South America may have played an important role in forming these and other similar disjunctions in the family. A number of well-supported clades are present, including Saxifraga s. str., Micranthes, Saxifragopsis/Astilbe, Chrysosplenium/Peltoboykinia, and the Boykinia and Heuchera groups. The use of additional characters has provided greatly increased resolution and internal support at deep levels. Saxifragaceae comprise two major lineages: Saxifraga s. str. (including Saxifragella) and all other genera of the family (the heucheroids). This major split is accompanied by general biogeographical and morphological differences. Whereas Saxifraga s. str. is largely arctic to alpine in occurrence, the heucheroid clade is largely temperate in distribution. Saxifraga s. str. has a relatively uniform floral morphology (generally actinomorphic; 5 sepals, 5 petals, 10 stamens, 2 carpels), whereas the heucheroid clade encompasses actinomorphic and zygomorphic forms, as well as variation in the number of sepals, petals, stamens, and carpels. Deep-level relationships within both Saxifraga s. str. and the heucheroid clade are well resolved and supported. A phylogenetic classification of the family is provided.

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