XVI International Botanical Congess

From the view-point of origin or early evolution of land plants, special attention has been paid to the hornworts, because they are considered to have some critical features. Recently, extensive studies based on the cladistic analysis of morphological, ultrastructural and biochemical data, and the phylogenetic analysis of nucleotide sequences have been made to clarify the phylogenetic relationships among major land plant groups, giving several different phylogenetic positions to the hornworts. In this paper we summarize the result of these recent investigations, and discuss the phylogenetic implications of some ultrastructural and biochemical features including chloroplast ultrastructure and phenolic constituents of the hornworts, supporting the hypothesis that the hornworts are the basal group of land plants.