Certified GKH Gardening Expert
Rhus and Toxicodendron a fairly easy to tell apart. This specimen is far too diseased to know, exactly, but the stems are too "tree-like" to be Toxicodendron (Poison Sumac) Generally, ornamental Sumac trees will have very slender leaves, while Poison sumac will have fuzzy and slightly irregularly shaped leaves that are wider.
Toxicodendron Sumac will grow as a small shrub, and usually prefer shade. Any tree labeled as "Sumac" will be Rhus, since there isn't a single nursery that would sell Toxicodendron. If you have purchased this tree, or it was planted on purpose, then it is likely just an ornamental Sumac tree.