XVI International Botanical Congess
Three genomes provide structural homologies for molecular and phylogenetic studies. For the nuclear genome, PCR has located fern homologues to developmental genes of angiosperms (the CKNOX gene in Ceratopteris).The chloroplast genome, conserved in gene content and order in most land plants, has some rearrangements which circumscribe groups.A large inversion in chloroplast DNA is shared with more derived plants except for lycopsids, marking them as the basal vascular plants. The higher leptosporangiate ferns contain a duplicated psbA gene and at least two inversions. For the mitochondrial cox2 gene, introns in many mosses, gymnosperms and angiosperms have been secondarily lost in pteridophyte taxa.Structural features may serve to correct spurious groupings from sequence analysis caused by long-branch attraction.