Opuntia fragilis (Nutt.) Haw. (Cactaceae) in the Bulgarian flora

Abstract Opuntia fragilis (Nutt.) Haw. (Cactaceae) is the smallest and most cold-hardy species of genus Opuntia in North America. In Bulgaria it is grown as an ornamental plant, but in 2019 a population of this species was discovered by other researchers in natural habitats in Lozenska Mt (Western Bulgaria) at 630–660 m a.s.l. on an area (extent of occurrence) of ca. 100 m2. In July 2020, we established a population of this species on the Black Sea coast near the town of Primorsko (Eastern Bulgaria) at 5 m a.s.l. on an area of ca. 300 m2. The distance between the two populations is 360 km in a straight line and their origins are independent of each other. The two localities of this species are so far the only ones described not only for the territory of Bulgaria, but also for Europe. Data are given on the conditions characterizing each of the localities. The possible reasons for the appearance in natural habitats of this alien plant species for the Bulgarian flora are considered. The impacts and threats this species may have on biodiversity in natural habitats are indicated. Measures have been proposed to control the populations of the species.