Black Walnut leaves are a brighter green as well - both at emergence and maturity. Tree of heaven leaves emerge reddish and are a darker green at maturity.

The bark is different too - Black Walnut bark has ridges and Tree of Heaven tends to be smoother, except on large specimens.

It's confusing in that mature specimens resemble each other so much. I noticed the red thing, which is what I've been going by for weeding, also the smell.

Black walnuts have a somewhat rank odor too, in my experience. (Pulled a few out of perennial beds today!?

+oM

I am also frustrated by this. We recently cut down a large black walnut tree (toxic to plants and dogs) but I swear what I'm pulling up are tree of heaven. The stems are a reddish brown, as are the top leaves. The leaves stink when touched and the roots typically bend out to the side. The leaves are not entirely smooth--they aren't serrated but have a ripple towards the stem. Am I right--are these tree of heaven?

If these are first year seedlings, you can dig down a couple inches and find the walnut shell pretty easily...the squirrels don't bury them very deep. If you have a lot to go through, you could at least use this method to help you learn to distinguish between the two.

Alex

When there are no leaves or fruit to look at, cut a small twig lengthwise and check out the pith -- the pulpy tissue in the center. In walnuts it's dark brown and broken up into crosswalls ("chambered"), in ailanthus it's continuous.

The easiest way to tell them apart is that the leaves of Tree of Heaven are smooth while Black Walnut leaves are serrated. Also, Tree of Heaven leaves have that peanut butter-like smell when crushed.