Opuntia humifusa (Raf.) Raf. (Cactaceae) in the Bulgarian flora

Abstract Opuntia humifusa (Raf.) Raf. is included in the List of Top 10 of the worst invasive alien plant species in Bulgaria. This is the fastest spreading species of the four species of the Opuntia genus found so far in natural habitats in Bulgaria. In the period 2010-2023, 3 new localities of the species were established in 3 new floristic regions of Bulgaria: Black Sea Coast (North), Stara Planina (East) and Strandzha Mountain. They describe the northernmost and easternmost distribution limits of the species in Bulgaria. The described localities are different in area: from 0.08 ha to 21.11 ha. The characteristics of the abiotic environment are presented such as: slope, exposure, elevation, bedrock, soil, climatic region and subregion. The habitats in which individuals of the species are found are indicated. Accompanying plant species were studied. The spatial structure of O. humifusa populations was studied. The reasons for the appearance and spread of this invasive alien plant species in territories that have not been inhabited by it until now have been examined, considering that these reasons are not natural, but have an anthropogenic character. Our findings support the opinions of other researchers about the key role of nature lovers in the spread of this invasive species. Factors favoring the increase in population size in established localities are indicated. Methods have been proposed to control the spread of the species.