ABSTRACT
In this chapter, the authors present analyses of an extensive set of small subunit rRNA gene sequences. All of the major lineages of green plants are represented, but the authors’ coverage of the land plants is especially dense. The main objectives of this analysis include reassessing whether land plants are monophyletically derived, identifying the nearest sister group to the land plants among the green algae and determining the relationships of the various lineages of 'pteridophytes'. The objectives also include the determination of the relationships among the main bryophyte groups and their relationships to other land plants. The evolutionary origins of land plants, and especially their major patterns of diversification, remain imperfectly known. The 18s data provide high levels of resolution among the major lineages of green plants. Many of 18s phylogenetic hypotheses are internally robust, but support for others is quite weak.
