| Summary: | Previous studies of the small Southern Hemisphere family Atherospermataceae have drawn contradictory conclusions regarding the number of transantarctic disjunctions and role of transoceanic dispersal in its evolution. Clarification of intergeneric relationships is critical to resolving (1) whether the two Chilean species, Laurelia sempervirens and Laureliopsis philippiana, are related to different Australpacific species, implying two transantarctic disjunctions as suggested by morphology; (2) where the group is likely to have originated; and (3) whether observed disjunctions reflect the breakup of Gondwana. We analyzed chloroplast DNA sequences from six regions (the rbcL gene, the rpl16 intron, and the trnL-trnF, trnT-trnL, psbA-trnH, and atpB-rbcL spacer regions; together 4,338 bp) for all genera and most species of Atherospermataceae, using parsimony and maximum likelihood (ML). The family's sister group, the Chilean endemic Gomortega nitida (Gomortegaceae), was used to root the tree. Parsimony and ML yielded identical single best trees that contain three well supported clades (>80% bootstrap): Daphnandra and Doryphora from south-eastern Australia; Atherosperma and Nemuaron from Australia-Tasmania and New Caledonia, respectively; and Laurelia novae-zelandiae and Laureliopsis philippiana from New Zealand and Chile, respectively. The second Chilean species, Laurelia sempervirens, is sister to this last clade. A likelihood ratio test rejects the molecular clock for the full rbcL data set, but the clock assumption holds for the ingroup. The atherosperm fossil record goes back to the Upper Cretaceous and includes pollen, wood, and leaf fossils from Europe, Africa, South America, Antarctica, New Zealand, and Tasmania. Calibration of rbcL substitution rates with the fossils suggest an initial diversification of the family at 100-140 million years ago (MYA), likely in West Gondwana, early entry into Antarctica, and long distance dispersal to New Zealand and New Caledonia at 50-30 MYA by the ancestors of L. ...
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