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The morphological characteristics of achenes of Lactuca serriola represented by 34 local populations from Slovenia and 12 local populations from Sweden were studied in relation to their eco- geographical conditions. In total, eight quantitative morphological characters were evaluated: length and width of achene body; index length/width of achene body; number of ribs on achene body; length of beak; length of pappus bristles; pappus area and discus diameter. Nested ANOVA analysis indicated significant differences in length and width of achene body, length of pappus bristles, and pappus area between Slovenian and Swedish populations. Achenes from Slovenia were longer, wider and possessed longer pappus bristles than achenes from Sweden. Among geographical factors, latitude had the greatest impact on the morphological characters evaluated. Significant differences in seven parameters were also found between populations within countries and between samples within populations. It is probable that this variation has a genetic basis with sufficient variation within populations to permit continued selection.