Systematic plant morphology and anatomy - 50 years of progress

Fifty years of comparative and systematic plant morphology and anatomy are reviewed. Thanks to new techniques (TEM, SEM, cinematography, molecular analyses), and new methods and concepts (cladistics, evolutionary paleobotany, molecular systematics and molecular developmental genetics), plant systematics and comparative structural studies saw major progress. The integration of micromorphological with molecular data has led to an increasingly robust phylogeny of the angiosperms. Successes and failures in the premolecular era of phylogenetic classification using morphological and/or anatomical markers only are illustrated with examples. With the new phylogenetic framework, it becomes possible to trace the evolution of characters more accurately than before. Central problems in comparative and systematic structural studies are the meaning of homology and character definition; some aspects have been elucidated but new ones have appeared with the molecular dimension in evolutionary biology. In vegetative anatomy, the integration of ecological and systematic anatomy into "ecophyletic" anatomy has led to a better understanding of the driving forces behind evolutionary diversification of wood and leaf anatomical attributes. However, the intertwining of ecological (extrinsic) and organisational (intrinsic) constraints in the origin of form remains a major challenge for future studies.