Erechtites hieracifolia (L). Raf. ex DC. is a species of American origin that spreads dynamically all over the world as a result of human activity. In the beginning of the 21^st century, the number of its localities rapidly increased in Central and Eastern Europe, particularly, in pine forests and degraded peat bogs, where the species grows profusely. It has become an invasive plant and its abundant occurrences are a serious problem in many places. This work shows the results of study on the variation of fruits in E. hieracifolia, at the individual, population and interpopulation levels, in the areas of its rapid spread over the pine forests of Poland and Ukraine. It was found that the range of variation at all analysed levels is very similar. However, a small separation of eastern European populations was observed. Also, the production of diaspores was evaluated at maximum 21,000 achenes per an individual.

Keywords: forest habitats, invasion, Natura 2000 areas, Poland, Ukraine, variability.