Which of the following is considered for natural system of classification?a. External featuresb. Ultrastructurec. Anatomyd. Embryology e. Phytochemistryf. Phylogeny

Natural classification systems were based on natural affinities among the organisms and consider, not only the external features, but also internal features, like ultrastructure, anatomy, embryology and phytochemistry. Phylogeny is considered in phylogenetic system of classification.