In this multidisciplinary thesis, thousands of plant species were screened to study their major foliar polyphenol groups and their distribution across the plant kingdom. While plants produce thousands of polyphenol compounds primarily for defensive purposes, current research has predominantly focused on health benefits of certain species and compounds, often employing variable methodologies. In contrast, older large-scale chemotaxonomy studies were limited by the methods available at the time. This study addresses these gaps by employing a comprehensive plant screening approach with updated and consistent methodologies throughout the data.

The first part of this thesis establishes a basis for extensive plant screening. A novel graphical method was developed to examine species-specific quantitative and qualitative variations in polyphenol profiles and their seasonal changes. It was observed that while the species expressed certain levels of quantitative variation, the polyphenol profile remained recognizable. The seasonal changes were relatively subtle and most of the changes were detected in the species producing ellagitannins and proanthocyanidins. Additionally, linking the polyphenol results to significant bioactivities revealed specific compound types that influence these activities. The findings from various plant species suggest that plant collection methods used in large-scale plant screening, which do not strictly define timing and use pooled samples from multiple individuals, effectively represent the species.

The second part of this thesis integrates chemical data from hundreds of plant families with contemporary plant phylogenies, providing a biological context for the chemical findings. It was observed that the distribution of eight polyphenol groups likely reflects key evolutionary events in plants at deeper phylogenetic levels, while ongoing ecological processes influence polyphenol profiles at lower levels closer to the species level. Flavonol derivatives, quinic acid derivatives and proanthocyanidins were the most widely distributed polyphenol classes, while hydrolysable tannins were even more restricted to specific clades than previously assumed. Within these main classes, the biosynthetically simpler subgroups were more frequently observed compared to biosynthetically later counterparts.