McLewin, Will (2006) Peony rockii and Gansu Mudan , available directly from his website, www.phedar.com. [Abstract: The formal name for these woody peonies, initially derived from Paeonia rockii is Paeonia Gansu Group. They have been the subject of many misconceptions, partly because they have been extremely difficult to obtain. White forms have usually been called something like 'Rock's peony' - an invalid and ambiguous name. They have been the holy grail of many gardeners on account of their magnificent scented flowers and their great rarity. In fact there are many different colours and forms and they are becoming readily available. This book explains their origins, dispels the myths and inaccuracies that have surrounded them and celebrates their glorious diversity. They are undemanding shrubs, rewarding and easy to grow. They will inevitably and rightly become much better known but the sheer splendour of their flowers is likely to ensure that as they become more common they will retain their legendary status.]

Color / Form classification

The classification categories of 9.1 lead to a natural ordering and a corresponding reference number for each cultivar that locates each in the sequence of pictures.