**Abstract**

We studied taxa from genus *Bidens*, *Solidago*, and *Erigeron*, sect. *Conyza* (Asteraceae). By analyzing the nucleotide sequences of the internal transcribed spacer (ITS1)-ITS2 site, the hybrid origin of the *Bidens decipiens*, previously attributed to the North American alien species *B. connata*, was confirmed. The analysis of trnL-trnF sequences showed that the native *B. cernua* is the maternal species and the invasive *B. frondosa* is the paternal species in all probabilities. Diagnostic morphological features of the three *Solidago* taxa growing together in the vicinity of Pskov have been studied: a native *S. virgaurea*, an invasive species of North American origin *S. canadensis*, and their hybrid *S. niederederi*. *S. niederederi* has an intermediate position between *S. virgaurea* and *S. canadensis*. The hybrid origin of *S. niederederi* is proven by molecular analysis of nuclear DNA nucleotide sequences (ITS1-ITS2 site). It is not yet possible to unambiguously answer the question which parent species is maternal and which is paternal. We also studied invasive species of the genus *Erigeron* sect. *Conyza* in the Mediterranean. Occasionally occurring in Southern Europe, individuals of *E. canadensis E. sumatrensis* with intermediate morphological features, described as "*Conyza rouyana*," are likely unstable and soon "absorbed" by the parent species *E. sumatrensis*. Contrary to the hypothesis by C. Elton explaining the success of plant invasion in a new homeland by strengthening hybridization processes in the secondary distribution range.

**Keywords:** hybrids, hybridization, invasive species, *Bidens decipiens*, *Solidago niederederi*, *Erigeron canadensis*, *E. sumatrensis*, ITS1-ITS2 site, *rpl32-trnL* intergenic spacer, *trnL-trnF* intergenic spacer
