Conflicting Phylogenies for Early Land Plants are Caused by Composition Biases among Synonymous Substitutions

摘要

Plants are the primary producers of the terrestrial ecosystems that dominate much of the natural environment. Occurring approximately 480 Ma (Sanderson 2003; Kenrick et al. 2012), the evolutionary transition of plants from an aquatic to a terrestrial environment was accompanied by several major developmental innovations. The freshwater charophyte ancestors of land plants have a haplobiontic life cycle with a single haploid multicellular stage, whereas land plants, which include the bryophytes (liverworts, hornworts, and mosses) and tracheophytes (also called vascular plants, namely, lycopods, ferns, and seed plants), exhibit a marked alternation of generations with a diplobiontic life cycle with both haploid and diploid multicellular stages and where the embryo remains attached to, and is nourished by, the gametophyte (Haig 2008). The interjection of a multicellular diploid phase into the land–plant life cycle was an important adaptation that enabled long-distance dispersal via mitotic spores where waterborne male gametes have restricted motility in dry terrestrial environments.