Cytological and morphological variation of Fallopia sect. Reynoutria taxa (Polygonaceae) in the Krivánska Malá Fatra Mountains (Slovakia).
Representatives of Fallopia sect. Reynoutria (knotweeds) belong to the most aggressive invasive plants in Europe. Despite their significant role in biological invasions and the major interest devoted to them by botanists and environmentalists, the identification of the members of this group is still very difficult and often mistaken. We studied the distribution of this group in the northwestern part of the Krivánska Malá Fatra Mountains (northwestern Slovakia). Forty-three Fallopia sect. Reynoutria stands (53 stems, 106 leaves) were used in flow cytometry and multivariate morphometrics to evaluate their genome size and morphological variation. Our research revealed that the group in the study area includes three knotweed taxa and that each of them is represented by only one cytotype: hexaploid (2n=6x ~ 66) in F. ×bohemica (23 stands), octoploid (2n=8x ~ 88) in F. japonica var. japonica (18 stands) and tetraploid (2n=4x ~ 44) in F. sachalinensis (2 stands). Morphometrics of 23 leaf characters revealed that the most reliable distinguishing character of Fallopia sect. Reynoutria taxa is leaf indumentum. Analyses showed that F. × bohemica is much more similar in leaf morphology to F. japonica var. japonica than to F. sachalinensis, thus explaining the fact that F. × bohemica is, in both Slovakia and Europe, very often confused with F. japonica var. japonica, whose presence outside cultivation is overestimated. Compared to the other two knotweed taxa, occurrences of F. japonica var. japonica in the study area were situated mainly along watercourses, due to its exclusively vegetative propagation.