Appears to be a herbaceous seedling. Do you have any other peonies in the area? As a seedling you can name it anything you want to. Some seedlings look so much better than either parent. I keep seeing the miniture tree form in herbaceaous but have not tracked it back to parentage. It does make it appear to be a tree peony but many as they age return to "normal".
Give it a sprinkle of fertilizer now. Say something with equal numbers then this September dig the plant up. Although it appears to be a seedling it could be posible that where it is used to be one of the places the previous home owner dumped their garden trash which could have included discarded peony roots. If the root is buried too deep perhaps this stem is the only one it has energy to send up. Until it is happy it will not flower. The flower may be nothing or it may be a jewel.
When we moved to this house in the woods behind one of the churches I found several plants growing that I dug up and took home. I found out later the church members had been putting their garden trash there to raise the soil level to extend the parking lot. In the same woods I have found other plants that people had dumped. You might see slightly raised places where you have found your other goodies.