DNA sequences from Miocene fossils: an ndhF sequence of Magnolia latahensis (Magnoliaceae) and an rbcL sequence of Persea pseudocarolinensis (Lauraceae).

We report a partial ndhF sequence (1528 bp) of Magnolia latahensis and a partial rbcL sequence (699 bp) of Persea pseudocarolinensis from the Clarkia fossil beds of Idaho, USA (Miocene; 17-20 million years [my] BP). The ndhF sequence from M. latahensis was identical to those of extant M. grandiflora, M. schiediana, M. guatemalensis, and M. tamaulipana. Parsimony analysis of the ndhF sequence of M. latahensis and previously reported ndhF sequences for Magnoliaceae placed M. latahensis within Magnolia as a member of the Theorhodon clade. This result is reasonable considering that: (1) the morphology of M. latahensis is very similar to that of extant M. grandiflora, and (2) a recent molecular phylogenetic study of Magnoliaceae showed that the maximum sequence divergence of ndhF among extant species is very low (1.05% in subfamily Magnolioideae) compared with other angiosperm families. We reanalyzed the previously reported rbcL sequence of M. latahensis with sequences for all major lineages of extant Magnoliales and Laurales. This sequence is sister to Liriodendron, rather than grouped with a close relative of M. grandiflora as predicted by morphology and the results of the ndhF analysis, possibly due to a few erroneous base calls in the sequences. The rbcL sequence of P. pseudocarolinensis differed from rbcL of extant Persea species by 3-6 nucleotides and from rbcL of extant Sassafras albidum by two nucleotides. Phylogenetic analyses of rbcL sequences for all major lineages of Magnoliales and Laurales placed the fossil P. pseudocarolinensis within Lauraceae and as sister to S. albidum. These results reinforce the suggestion that Clarkia and other similar sites hold untapped potential for molecular analysis of fossils.