Relationship between the floristic dissimilarity of native and alien floras of studied river ports and the geographical distance of ports of the individual waterways. A. Elbe-Vltava waterway. Regression lines for native species (Y = 45 + 0.012X; R2 = 0.111; p = 0.0025) and two categories of alien species: archaeophytes (Y = 41 + 0.013X; R2 = 0.081; p = 0.007) and neophytes (Y = 46 + 0.013X; R2 = 0.082; p = 0.0082). B. Danube waterway. Regression lines for native species (Y = 44 + 0.019X; R2 = 0.292; p = 0.0001) and two categories of alien species: archaeophytes (Y = 34 + 0.019X; R2 = 0.279; p = 0.0001) and neophytes (Y = 43 + 0.026X; R2 = 0.420; p = 0.0001).