About Rockii…Paeonia rockii is a Chinese species which has white flowers with dark basal flares. As a species it occurs naturally in the wild. There are numerous hybrids which incorporate P. rockii in their genetic lineage and are often referred to as “rockii hybrids”. The term “rockii Hybrid” is accurate to a certain extent as these cultivated plants have most certainly originated from crosses with other species or plants from the P. suffruticosa group. However, they can no longer be considered the species Paeonia rockii due to their cultivated origins.
About Suffruticosa…Paeonia suffruticosa is no longer recognized as a species, but rather a hybrid swarm made up of many named cultivars and numerous seedlings. Through genomic work we now know P. suffruticosa is a hybrid involving the following species: P. cathyana, P. decomposita, P. ostii, P. jishanensis, P. qiui and P. rockii. Thus P. suffruticosa is now relegated to a group of plants with divergent, but somewhat common ancestory and common characteristics.
Hybrids of P. rockii…Much confusion exists! Dark flares and leaf structure alone may not be an accurate identification method, but is commonly and inappropriately used to do so. Flares are a trait of any number of species (P. delavayi variants often express flares). Foliage structure can be quite divergent as well in other groups, appearing to be similar to P. rockii. All said, visual observation is seldom enough to conclude whether a cultivar has its origin with P. rockii. Additionally, many of the historic Chinese and Japanese P. suffruticosa cultivars certainly have P. rockii in their lineage, but there is no evident expression of flares and foliage often associated with the species. The best classification again is to place these hybrids within the Suffruticosa Group.
Registration of P. rockii hybrids…As noted above, rockii hybrids most certainly fall outside the boundaries of a species, thus they cannot be called species selections, but are rather P. suffruticosa group plants. For purposes of APS cultivar classification, this places rockii hybrids in the Suffruticosa Group. It is a term that has long been used by the APS (and in commerce), to differentiate between cultivated woody peonies that have some component of Delavayanae in them (the Lutea Hybrids Group) and those that do not (the Suffruticosa Group). We can also think of the Suffruticosa Group as containing those cultivated peonies that arise out of the Vaginatae. Using Suffruticosa for this group harkens back to 1804 when Andrews published the name in describing what has been determined to have been a garden peony brought from China, rather than an actual species.
In the International Code of Nomenclature for Cultivated Plants, a Group is a formal category which may comprise cultivars, individual plants or combinations thereof on the basis of defined character-based similarity. The criteria for forming and maintaining a Group vary according to the required purposes of particular users. In the case of peonies, the users are the APS itself (for purposes of forming a show schedule), and vendors and gardeners (for the purpose of communicating and understanding broad characteristics of a named cultivar).
While this may be a bit confusing, cultivars designated as Suffruticosa Group peonies may have in their descriptions indicating influence from the species P. rockii. Those which lack an observable influence will likely make no mention of this in the Peony Registry description.