PHYLOGENETIC-RELATIONSHIPS OF CONIFERS INFERRED FROM PARTIAL 28S RIBOSOMAL-RNA GENE-SEQUENCES

The conifers, which traditionally comprise seven families, are the lar gest and most diverse group of living gymnosperms. Efforts to systemat ize this diversity without a cladistic phylogenetic framework have oft en resulted in the segregation of certain genera and/or families from the conifers. In order to understand better the relationships between the families, we performed cladistic analyses using a new data set obt ained from 28S rRNA gene sequences. These analyses strongly support th e monophyly of conifers including Taxaceae. Within the conifers, the P inaceae are the first to diverge, being the sister group of the rest o f conifers. A recently discovered Australian genus Wollemia is confirm ed to be a natural member of the Araucariaceae. The Taxaceae are neste d within the conifer clade, being the most closely related to the Ceph alotaxaceae, The Taxodiaceae and Cupressaceae together form a monophyl etic group. Sciadopitys should be considered as constituting a separat e family. These relationships are consistent with previous cladistic a nalyses of morphological and molecular (18S rRNA, rbcL) data. Furtherm ore, the well-supported clade linking the Araucariaceae and Podocarpac eae, which has not been previously reported, suggests that the common ancestor of these families, both having the greatest diversity in the Southern Hemisphere, inhabited Gondwanaland.