Abstract: The two invasive Reynoutria species, R. japonica var. japonica, R. sachalinensis and their hybrid R. x bohemica are often misidentified by managers and non-specialists. The taxonomic confusions are all the more exacerbated by the infraspecific variability of introduced populations, in terms of morphology, genetic diversity and ploidy level. We resolved the identity of North-Eastern French invasive populations using 4,582 SNPs from a RADseq analysis, DNA contents estimated by flow cytometry and 12 vegetative morphometric variables. The SNPs supported only one single genotype for R. japonica over 11 localities, while the nine localities of R. x bohemica represented by one genotype each. Estimation of genome size using DAPI-staining and flow cytometry revealed only octoploid cytotypes for R. japonica and hexaploid cytotypes for R. x bohemica, whereas R. sachalinensis was represented by tetraploid and hexaploid cytotypes. Among morphometric variables, no single one allows for a clear differentiation of the three taxa. We propose a combination of characters to easily and quickly identify these three invasive taxa based on six vegetative criteria including leaf and apex length, as well as leaf shape, leaf base and apex shape, and the extrafloral nectaries on the node.

Key words: Fallopia spp., flow cytometry, invasive plant species, morphometric analysis, population genetics, RADseq, Reynoutria spp