Flowering plants (angiosperms), with about 300,000–400,000 living species, are the largest and most diverse assemblage of land plants on our planet. They include many familiar and economically important plant groups such as the cereal grasses, legumes, and most fruits and vegetables. One of the major goals of systematic botany is to reconstruct the evolutionary history of this diverse lineage. Traditionally, hypotheses of evolutionary relationships have been based largely on morphological traits (for example, flower structure, stem anatomy), but current approaches also consider genetic evidence from one or a combination of the three genomes found in plants (plastid, mitochondrial, and nuclear). This type of work has provided many important insights into flowering plant evolution, and there has been substantial progress in reconstructing the plant tree of life. This knowledge has necessitated the production of a new classification scheme because some families and higher taxa were found not to be natural, and this framework now provides a solid evolutionary basis by which all aspects of comparative flowering plant biology can be focused.