OAK IDENTIFICATION

Where to start with oaks?

The genus Quercus (Latin for – shocker – “oak”) is part of the beech family, Fagaceae, and includes over 500 species spread across the northern hemisphere, with North America having the greatest diversity and species richness. The continent has a sort of axis of oak abundance, species-wise; the further south, the more there are. The whole of Canada boasts about a dozen species. Mexican botanists, on the other hand, have to contend with about 160 species, and genetic analysis suggests there are many more unrecognized members of the genus to be found in the wild. The US contains around 90 species, and here in the southeast-central states, there’s around 20 or so, a respectable number to know without it being overwhelming.

Part of the trouble with identifying oaks is that they’re very messy, taxonomically speaking. Within the genus, there are two subgenera, Quercus and Cerris, which in turn each have various sections determined by botanic characteristics and genetic analysis. Fortunately for our purposes, there are really only two sections which require examination: Lobatae; the red oaks, and Quercus, the white oaks.

Within sections, oaks tend to hybridize freely with each other. So Lobatae, which has about 10 distinct species in Kentucky, also has a number of naturally occurring hybrids, all with their own names. Quercus x runcinata, for instance, is a hybrid between the northern red oak (Q. rubra) and the shingle oak (Q. imbricaria). That’s what some people would have you believe, at least. Another school of thought suggests that most supposed hybrid specimens are merely unusual members of an established species.

All this is to say that oaks display a truly impressive range of morphological characteristics. Not only within the genus, the subgenera, the sections, and the species – two leaves from the same tree can look quite distinctly different from each other. How does one even begin to sort them out?

Fortunately, oaks provide a few different clues that can help narrow down to a recognized species with a fair degree of confidence...