Paeonia rockii is a species of tree peony which is native to China's northwest. Cultivated tree peonies which are derived from this species are assigned the cultivar group know as ziban mudan 紫斑牡丹, or "purple-flare tree peonies". In English langauge sources this cultivar group in sometimes given as 'Gansu Mudan' or 'Gansu tree peonies.' The flowers of these plants are above all distinguished by dark flares at the base of the petals. We consider these some of the finest tree peonies one can grow; they are vigorous and disease resistant, typically with a wonderful fragrance.
Gansu province is located in China's northwest. It has an arid climate, with hot summers (100+ °F) and cold winters (below 0 °F). Though geographically isolated, it has an ethnically mixed population of Chinese, Tibetans, as well as Turkmen and Hui Muslims. This diverse population is a legacy of Gansu's location; the Silk Road passed through the province and merchants from across Eurasia left their mark. The Buddhist cave complex at Dunhuang with it's lavishly painted murals and the spicy 'pulled noodle' soup are two of the province's most famous cultural artifacts.
For gardeners, Gansu is also notable as being one of the areas of China where the species Paeonia rockii is found in the wild. Visiting Gansu, it is amazing that tree peonies could thrive in such a seemingly inhospitable location. This species of tree peony was introduced to the West in the 1920s by the botanical explorer Joseph Rock. He is often credited with 'discovering' the plant and white rockii tree peonies are sometimes referred to as 'Rock's Peony.' Using such language discounts the fact that these tree peonies were appreciated by the locals in Gansu province long before the arrival of a botanist from Harvard's Arnold Arboretum.
In some cases, tree peonies in Gansu province really are trees. Here, Kasha Furman, owner of Cricket Hill Garden, stands before an 80 year old specimen tree peony in Lanzhou, the provincial capital. It's over 9' tall and 12' wide!