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!

Tree peony cultivation in Gansu province has undergone a renaissance in the last half century thanks in large part to the passion of one dedicated breeder. Chen Dezhong, shown above, was an idealistic youth in the summer of 1961 when he answered Chairman Mao's call for 'educated urban youth to go and work in the mountain areas to strengthen agriculture.' He left his clerical job in the city and returned to his rural home village of Peace, in the parched countryside outside of Lanzhou. His goal was to transform the barren hills into verdant country. He settled on tough, drought tolerant tree peonies as the best plants to achieve this.
In his nursery, the Peace Peony Garden, he collected peonies from throughout the province as well as the rest of China. He has grown out tens of thousands of seedlings and selected and named the best of these. His cultivars combine the vigor and toughness of native Gansu peonies with the wide variety of form and color associated with more traditional Chinese tree peonies. We imported many of these superior cultivars in the early 2000s. They have thrived in our nursery and will do the same in your garden! 
Some of our favorite rockii cultivars:
Snow Lotus  雪蓮 Xue Lian
Magical Red Haired Woman 紅髮魔女 Hong Fa Mo Nv
Red Crown with Jade and Pearls 紅冠玉珠 Hong Guan Yu Zhu
Cup of Shining Night  夜光杯 Ye Guang Bei
Purple Jade Orchid  玉蘭紫 Yu Lan Zi