To some degree, tree identification can be done with one leaf. I think this depends on a variety of factors though. Some plants just have leaves with more easily identifiable characteristics than others. I can tell without a doubt, the leaf posted was mulberry. I’m not as good when it comes to distinguishing between pecan and black walnut. I don’t know that I can always determine each species of oak from my area (they hybridize terribly), but I can identify most of the trees where I live. Get me away from my area though,,,,,,,,,,
Here are most of leaf variations of the mulberry found on my place. As you said Sean, "It works sometimes". Curtis