The Intersectionals or ITOH peonies are rare crosses between yellow hybrid tree peonies and a blush P. lactiflora
bringing true deep yellow and other fine colors to herbaceous peonies. All flower mid-season.
[From Paeonia:] Intersectional hybrids are the newest peony hybrids. They are created by crossing peonies from one section with peonies from another section of the genus. Thus the name inter-sectional hybrids. For generations, such crosses were believed to be impossible. Professor A. P. Saunders (1869-1953), America's greatest peony hybridizer, considered this cross "the impossible dream".
[From Peonies, by Jane Fearnley-Whittingstall, p. 63:] In the 1960s Toichi Itoh crossed the low-growing tree peony 'Alice Harding', a hybrid of P. lutea with the lactiflora 'Kakoden'. Sadly he did not live to see the seedlings flower. Four of them, 'Yellow Emperor', 'Yellow Crown', 'Yellow Dream' and 'Yellow Heaven' have since been produced commercially and caused great excitement. Yugen Higuchi has carried on the work in Japan, and the American Peony Society has now declared the new category valid under the name 'Itoh hybrids'.