Hierarchical clustering of the 1,170 histone-modifying TCM medicinals and the 18 modifications. A row represents a medicinal and a column a modification. The lighter (darker) the shade, the more potent the medicinal is to activate (inhibit) the modification. Modifications are close within clades in the upper dendrogram if they are similarly utilized among the medicinals. Refer to Table 1 for the abbreviations of the modifications.