Phylogenetic relationships among the four major lineages of land plants (liverworts, mosses, hornworts, and vascular plants) remain vigorously contested; their resolution is essential to our understanding of the origin and early evolution of land plants. We analyzed three different complementary data sets: a multigene supermatrix, a genomic structural character matrix, and a chloroplast genome sequence matrix, using maximum likelihood, maximum parsimony, and compatibility methods. Analyses of all three data sets strongly supported liverworts as the sister to all other land plants, and analyses of the multigene and chloroplast genome matrices provided moderate to strong support for hornworts as the sister to vascular plants. These results highlight the important roles of liverworts and hornworts in two major events of plant evolution: the water-to-land transition and the change from a haploid gametophyte generation-dominant life cycle in bryophytes to a diploid sporophyte generation-dominant life cycle in vascular plants. This study also demonstrates the importance of using a multifaceted approach to resolve difficult nodes in the tree of life. In particular, it is shown here that densely sampled taxon trees built with multiple genes provide an indispensable test of taxon-sparse trees inferred from genome sequences.alternation of generations ͉ hornworts ͉ liverworts ͉ phylogeny ͉ taxon sampling T he origin and early evolution of land plants (embryophytes) during the mid-Ordovician to lower Silurian (480-430 million years ago) initiated the establishment of the modern terrestrial ecosystems and fundamentally altered the course of evolution of life on earth. Two important events marked this period of unprecedented innovation in plant evolution: the massive colonization of the land by plants descended from charophyte algae and the change of the dominant generation in the plant life cycle from a haploid gametophyte to a diploid sporophyte (1-5). The first event opened a vastly underexplored niche of high-intensity solar radiation and abundant CO 2 to photosynthetic life. The second event conferred on plants two abilities to adapt to a life in a water-deficient and UV-abundant terrestrial environment. One is the ability to produce a large number of genetically diverse gametes to ensure fertilization on land where sperm locomotion is hindered, and the other is the ability to mask deleterious mutations through the dominantrecessive interaction of alleles, thus allowing a large number of alleles to persist in the gene pool (2-4). Our understanding of these events hinges on our knowledge of relationships between the organisms involved in these major evolutionary transitions. Despite numerous studies using diverse approaches analyzing morphological and͞or molecular characters, relationships among early land plants remain controversial (5-19). Fossil evidence, although increasingly improved, has not helped to resolve the issues decisively (20,21).A multitude of phenomena characterizing diversification of many major clades o...

No abstract

No abstract

No abstract

In phylogenetic trees generated from partial trnL(UAA) intron sequences, the hornworts (represented by nine species from the genera Anthoceros, Dendroceros, Megaceros, Notothylas and Phaeoceros) are resolved as a monophyletic group and are separated from the clades of mosses, liverworts and tracheophytes. A secondary structure of the trnL(UAA) intron of Anthoceros agrestis is presented, displaying the arrangement of the stem-loop regions P1-P9. Compensatory base-pair changes (coevolutionary sites) are detected in regions P4/5 and P9 within the hornwort sequences. The original homology of the most variable region, P8, cannot be detected anymore due to the extremely fast divergent evolution of this segment in the major land plant groups. Similarly, a high sequence divergence occurs in the trnL-trnF intergenic spacer. Apart from synapomorphic substitutions in the trnL(UAA) intron, the hornworts are characterised by a large P6 region consisting of many repetitive elements. The molecular data therefore support the hornworts as representing an independent land plant lineage (Anthocerotophyta). Although relationships between hornworts and the other land plant groups remain unresolved in the trnL(UAA) intron trees, it is rather unlikely that bryophytes are monophyletic in their traditional circumscription, i.e. comprising hornworts, mosses and liverworts.