I'm a relative newbie with Tree Peonies, but have been ramping up my 'research' into them. A trip to a botanic garden at just the right time revealed some beautiful 'moutan' types. Amazingly beautiful.
Looking at photos on websites, I'm struck by how different the flowers can look from one garden to another. I've also heard that plants can be mis-labelled as well.
I found 'Yaso Okina' to be - possibly - the most beautiful white tree peony I've seen so far. Here's my photo of it in bloom on May 1st at the Brooklyn Botanic Garden. Unfortunately, I've not found it for sale on any website, and I've only found reference to it as one of the parents of 'Alice Harding,' a yellow tree peony.