| Summary: | Inter- and intrapopulational morphological variability of Elymus repens, a cool-season peren-nial grass and a tenacious weed that spreads both by seeds and rhizomes forming a thick and stout net, was examined. Multivariate statistical analysis of 48 initial morphological characters obtained from 44 population samples (1180 specimens) collected in different habitats revealed the conspicuous variation within E. repens. Principal Component Analysis revealed three extremes of the morphological gradient that were referred to as three varieties of E. repens: var. repens, var. aristatus and var. subulatus, not correlated with the habitat type or geographi-cal location. Canonical Discriminant Analysis proved the taxonomic usefulness of characters such as awned or awnless glumes and lemmas as well as the shape of glumes for variety di-stinction. Results of morphological analysis, in relation to the low level of genetic variation showed in the previous studies, suggest that the extensive morphological variation of E. re-pens can be caused by its plasticity where different morphological patterns are realized on the same genome basis. Additionally, the open-pollinated system of mating results in new combi-nations of morphological characters of plants that further reproduce vegetatively by rhizomes. The nomenclature, taxonomic descriptions and a key to the three varieties are provided.
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