Turns out the Smoketree or Smoke bush (Cotinus coggygria
and Cotinus obovatus) is closely related to the sumacs (Rhus). It's in the family Anacardiaceae (the cashew family or the sumac family), and apparently produces urushiol, the toxin in poison ivy, oak, sumac, etc. Which is to say, if you are growing one, and you prune it, you may end up with a rash on your arm.