Any book that describes popular cultivars would have this information such as Allan Rogers book Huge flowers have been developed in both tree and herbaceous cultivars as attested for example here or in any collection with the herbaceous cultivars of the classic type that were developed to use as cut flowers such as Sarah Bernhardt which has flowers up to 9 inches across Using the terms intersectional and Itoh interchangeably some might beg to restrict the term Itoh to a subset there are cultivars with more or less tree peony habit like Souvenir du Professeur Maxime Cornu name simplified now to Maxime Cornu and those that die to the ground each year like Bartzella