The classic definition of demarcating a Scarlet Oak leaf is that its deep sinuses have a "C" shape with three to seven lobes, while those of a Pin Oak have a "U" shape with a similar number of lobes. Hybridization among members of the Red Oak Group, variability of individual leaves on the same twig, natural genetic diversity of the species, and the sad fact that plants obviously cannot read textbooks create problems for absolute identification of many plants, including this actual Scarlet Oak.