Quercus macrocarpa | Stanford
This photo shows the somewhat odd central structure of one of the Stanford Bur Oaks. The great age of the tree is shown by the depth of the bark furrows and the prominence of the bark ridges. One of the truths of oak identification, especially when the trees are planted far from their native range, is that any identifying trait has a very wide range of expression, so the notion of an identifying trait has to be held rather loosely. It's common from trees planted far from their native range to have been collected from an arboretum or other mixed oak area, leading to the confounding feature of oak reproduction, their ready willingness to hybridize. Sometimes oaks are referred to as promiscuous, given their ready willingness to exchange genes with any oak of the same subgroup, and occasionally beyond. To become proficient in oak identification requires a taste for chaos, and an eye for subtle pattern.