I found these beautiful mushrooms while walking in the woods near my house. They were growing on a fallen Elm limb. I returned twice to let them grow before I picked them and brought them home for closer observation. I believe they are Pleurotus citrinopileatus. However, I would have more confidence if this was a mushroom known to grow in my region. My best guess is that they have escaped captivity ;). I loved to hear some opinions from other observers.