Rock's peony or Rock's tree peony (Paeonia rockii, also Paeonia suffruticosa subsp. rockii) is a woody species of peonythat was named after Joseph Rock. It is one of several species given the vernacular name tree peony, and is native to themountains of midwestern China, mainly in Gansu and adjoining provinces. In Chinese, it is known as (pinyin: mu dan) or (pinyin: mu dan pi), and its flower is called(pinyin: mu danhua). It became the unofficial national flower of China following a nationwide referendum in 1994.