Abstract:From April to June in 2019, a naturalized population of Opuntia cespitosa was first found at Qiushan Hill, Guozhuang Town, Jurong City, southwestern Jiangsu. The population mainly occurs on an abandoned quarry at elevations of 46-90 m, covering an area of ca. 13.26 hm2, 510 m long from east to west, and 260 m wide from north to south. A total of 910 mature shrubs bearing flowers and fruits have been recorded there, among which the longest axis of the largest shrub consists of 10 continuous cladodes, indicating an age of 10 years, which probably appeared at Qiushan Hill in 2010. This naturalized population may be derived from the pot plants of O. cespitosa, which were possibly discarded in situ by the staff of Qiushan quarry, when the quarry became abandoned. The morphological features are compared between O. cespitosa and known other four naturalized species of Opuntia in China, and a key to these species is prepared. Furthermore, the dispersal mechanisms and its invasion risk of O. cespitosa are also discussed.