Important physical characteristics, morphological attributes, physiological functions, and genetic properties of mutant tanoak, Notholithocarpus densiflorus f. attenuato-dentatus (Fagaceae), and normal tanoak, Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S. H. Oh, were studied on the Challenge Experimental Forest in Yuba Co., California in an attempt to explain the cause of the mutation and to determine where in the tree it was manifest. Leaves, stomata, trichomes, foliar nutrients, photosynthesis, transpiration, internal moisture stress, DNA, and genetics (metabolonics) all were examined in detail. In some instances, the plant part or the process favored the mutant; in others, the normal tanoak exceeded. Susceptibility to Phytophthora ramorum, the sudden oak death pathogen (SOD) was similar. No all-encompassing functional difference for either type was indicated, other than the size and shape of the leaves and the metabolites in them. We know the two tanoak types differ genetically, but more complete genomic analysis is needed to pinpoint the cause of the mutation. Some thought-provoking enigmas concerning the morphology and physiology of tanoak are presented along with the status (number of plants and location) of the rare mutant.