Xanthium orientale L. (Asteraceae) as an invasive species in Ukraine: its distribution and ecological characteristics

Xanthium orientale L. is one of the most aggressive invasive plant species in Ukraine. Itstrongly transforms natural and anthropogenically disturbed habitats, especially in riparian landscapes. This study aimed to analyse the distribution, biotope affiliation, ecological characteristics, and phytosociological role of X. orientale in Ukraine. The analysis integrated herbarium collections, published literature, online biodiversity databases, and 67 geobotanical relevés collected from 2021 to 2025, comprising a total of 1137 localities. Vegetation classification was performed using the Braun–Blanquet approach. Ecological preferences were assessed using phytoindication methods, and differences between vegetation units were tested with the Mann–Whitney U test and visualised using box-plot diagrams. Two main vegetation types involving X. orientale were identified: the floodplain-associated Bidenti frondosae– Xanthietum albini and ruderal derivative communities dominated by X. orientale with Elytrigia repens. The species was recorded across ten vegetation classes, demonstrating high ecological plasticity. Phytoindication analysis revealed significant differences between the two syntaxa in moisture, soil carbonate content, and temperature regime, indicating habitat differentiation and niche expansion. The results confirm the high invasive potential of Xanthium orientale in Ukraine and emphasise the need for continuous monitoring and targeted management, particularly in river valleys and floodplain ecosystems.