Quercus engelmanii | Santa Rosa Plateau
The reality of Engelman Oak leaves, collected in-habitat on the Santa Rosa Plateau, shows a rather more varied story, as can be readily seen in this photograph. These leaves were informally collected as typical leaves from more than a half-dozen specimens. A similar survey of the closely-related oaks of the Southwestern United States yields a surprisingly similar, if slightly broader, range of leaf shapes, and also a wider range of colors. It's almost as if the oak species of the Southwest US got marooned in coastal southern California, and spent several millennia interbreeding. Which appears, from the geological and archaeological record, exactly what happened.