Black walnut foliage has a distinctive sweet smell that is unmistakable. Find a mature black walnut and take a good long whiff of the leaves, and you'll never forget the scent. It isn't unpleasant at all.

Plus, walnut leaves and twigs are soft to the touch and sort of fuzzy. Hickory leaves are stiffer and shinier, and the young twigs don't have that downy coating.

Hope this helps, you can google the info for pictures.

You can also post this question on the trees forum - those guys are pretty helpful and this question has come up before.

Id like to know if its possible to identify the bitternut (that's what we called them anyway) versus the hickory nut. The look exactly the same to me.

Steelskies, might help to narrow down the species you are interested in. Bitternut hickory is the name usually applied to Carya cordiformis, which is also known as yellow-bud hickory. Even when very young they will have sulfur yellow buds at the end of the shoots this time of year. The most common edible hickory we get around here is shagbark, which is easy to identify because of the very loose, shaggy bark on older trees. Younger trees are more difficult but you can rule out C. cordiformis by looking at the buds.