The screenshot above results from launching CDTree with the 'Interactive Display' buttons on the CDD page for the RNR_PFL domain hierarchy. Ribonucleotide reductase (RNR) and pyruvate formate lyase (PFL) are structurally similar and are thought to have diverged from a common ancestral domain. CDTree has been designed to discover and explore such relationships in detail, and is a central tool used to craft all of the curated domain hierarchies in the CDD.