And I guess greenlarry means acorn "shape, size and characteristics" rather than just type. For the acorn, you often need not just the acorn but also the cap.

Twigs and bark can be helpful too but are not always necessary.

Leaf shape gets you started. Acorns get you closer. And you need the cap on the acorn, because some of the differences come down to how far the cap covers the acorn.

But then you have natural variation within a species and the tendency of oaks to cross pollinate rather freely, as long as the growing range overlaps. So if you look for nice neat clear deliniations, you will go crazy.

everybody's favorite author, Dirr, has decent line drawings of a fair number of species. Symonds is a decent author for general tree id. And every library has some kind of trees of whereever it is you live, be it eastetn north america, rocky mountains, british isles, or the alaskan archipelago.

Get a couple books that have a format you can understand, grab a few leaves and acorns, and spend some quality time with words like auriculate, involucre, and my personal favorite, peduncle.

To be blunt, look at the variation in humans and both my European ancestors and the Eskimo ancestors are obviously the same species.

The difference in many oaks seems to be splitting hairs. It is more difficult than telling the difference between "british" humans and "sweedish" humans.

ken

Understanding that all US oaks are grouped in either the "red oak" group or the "white oak" group, the first think I would do is use the leaf to identify which group it is in. That cuts your identification universe down almost in half.

Look for bristle tips on the end of the lobes of the leaves; if tips exist, it is in the red oak group.

Here's a good article from Ohio: http://fieldbioinohio.blogspot.com/2011_12_01_archive.html