The genus paeonia as a whole, in the wild and in cultivation, has provided ample opportunity for misinformation and ambiguous names. This has been thoroughly, but not exhaustedly, alas, utilised. So some basic information seems appropriate.
For many years peonies separated neatly into two sections- herbaceous and woody. Woody peonies have unfortunately acquired the name ‘tree peonies’, which is understandable but inappropriate because they are not trees but clearly are shrubs. So shrubby peonies would be a better name, but as they originate in China, much better still is their simple and unambiguous Chinese name ‘mudan’.
There has ‘always’ been a curious link betwen mudan and herbaceous peonies because herbaceous tubers are usually used as the understock for grafted mudan scions.* However a more direct link is the relatively recent introduction of intersectional, or Itoh, hybrids between hebaceous peonies and mudan. Initially direct hybrids, the distinction between the now three groups will become blurred as back crosses are used.
*This has implications for moving and posting plants. Mudan make new root in September/October and are best not bare-rooted for posting after then, whereas herbaceous peony divisions can be moved until the end of March.
Both mudan and herbaceous peonies (and plant genera in general) fall naturally into identifiable groups or sub-sections. The two immediate sub-sections are always (true) species and hybrids, which immediately raises a major problem. Neither ‘species’ nor ‘hybrid’ is a defined or fully understood concept, but having at least made the point here, we gloss over it (like everyone in commerce or the media does), but see the hellebore pages and P. rockii below for some further comments.
The main groups within mudan are suffruticosa, delavayi and gansu, and a group of assorted disparate species including, szechuanica, jishanensis, qiui and ludlowii. Peony Gansu Group, developed relatively recently in NW China, consists of plants involving P. rockii and sharing some of its characteristics, notably hardiness, drought resistance when established and the striking purple to black blotch at the base of the petals.
P. rockii itself is a truly rare plant, not least because the vast majority of plants labelled as such, or as P. Joseph Rock or Rock’s Peony, are not P. rockii. Some, including the famous plant at Kew and at other eminent botanic gardens, have incorrect characteristics and are clearly P. Gansu Group hybrids. Others, those with correct morphological characteristics, could, and should, be labelled ‘P. rockii type’, and would be none the worse for it. Others, with ‘slightly different’ (or very different for that matter) characteristics, including the most widely distributed wrongly named example (given the name P. ‘Highdown’ in PRGM) are still superb, opulent garden plants. The details of what is a genuinely complex history and a comprehensive and irrefutable explanation are in PRGM (see books).
P. Gansu Group: a wide range of colour, form and size, some with names, mostly not. (Names in Chinese (pin yin). Fanciful English names are, strictly, invalid and mostly for commerce. Plants available are propagated (adventitiously) by division (not grafted) so all are on their own roots and vary greatly in size and price. Around £30 for a plant that will flower as soon as it is well established. Some small divisions of ‘true’ P. rockii (with wild provenance) are usually available.
Also a few Itoh peonies and a few herbaceous peonies, mostly species.
Email directly for the current list, also for the current peony seed list.
Plants available are mostly in 15l pots so can be collected any time by arrangement or posted bare root in moss at the appropriate time.