New records on chromosome numbers in non-native Erigeron L. taxa (Asteraceae) from Poland

The genus Erigeron (Asteraceae) includes several widely distributed invasive species for which data on chromosome numbers and cytological variation are lacking in many parts of their introduced range. In this study, we targeted five alien Erigeron taxa occurring in Poland to test their chromosome numbers in the context of cytological diversity and invasiveness. In addition, we included three native taxa of the E. acris s. l. complex which are also cytogeographically poorly recognised. To count chromosomes, we made stained microscopic preparations from root tip samples obtained from seedlings or mature plants. Among alien taxa, we documented diploids (2n = 2x = 18) in E. canadensis and E. ×huelsenii (a hybrid between E. acris and E. canadensis), triploids (2n = 3x = 27) in E. annuus, triploids and tetraploids (2n = 4x = 36) in E. strigosus, and hexaploids (2n = 6x = 54) in E. sumatrensis. In the case of native taxa, we found diploids (2n = 2x = 18) in E. acris subsp. acris, E. acris subsp. podolicus and E. muralis. We also showed that the karyotype of E. ×huelsenii includes two sets of chromosomes differing in size, reflecting the difference in the amount of nuclear DNA between its parental species. However, this hybrid appears to be a weak competitor due to its sterility, lack of vegetative propagation and short lifespan. Moreover, our results confirm that E. strigosus can be cytologically diverse even in one small geographical region in its introduced range. Further studies are needed to prove the effects of hybridisation and polyploidy on competitive abilities in alien Erigeron species.