Research on the base composition has long tradition in microbial research where base composition represents a significant classification criterion and similarly to genome size it represents an important predictor of species ecology. A similar research on the magnitude and dynamics of genome evolution in respect of base composition (DNA quality) is widely lacking in plants. Here we present results of measurements of GC content and genome sizes across a nearly complete phylogenetical family representation of monocots. This model group shows an extreme genome diversity comprising both species with absolutely lowest (Cyperaceae clade) and highest (Poaceae, Xyridaceae+Eriocaulaceae clade) GC contents known to date. The results of our pilot analyses using phylogenetical comparative methods are present which test how speed of GC content and genome size evolution may vary across various lineages of monocots and climatic regions, and to what extent the speed of genome evolution may be determined or reflected with specific life strategies and species ecology.