Gansu tree peonies are a subset of the suffruticosa group that are distinguished by their purple flare at the center of the flower. These incredibly hardy plants are from the Gansu region of China. The are often referred to as Rockii peonies as Joseph Rock helped to make them famous outside of China. These plants are very fast growing for tree peonies and become quite large, up to 7 feet tall. This group has thin billowy leaves that give a more informal appearance. They tend to cross pollinate and produce wonderful seeds that can be grown into new cultivars. These plants are of special significance to those in horticultural zones 2-3 as they are more cold tolerant . They are also particularly useful in areas with little direct sun as they flower profusely even with little light. The gansu peonies at Peony's Envy tend to benefit tremendously from this fact as the areas they are in can be quite shady.