Differences in the percentages (i.e. median, 25th and 75th percentile and min/max values) of core alien ornamental taxa (i.e. frost-resistant cultivated plants that persisted for a long time after abandonment or taxa that occur at many sites) within clusters of classified settlement types and within the unclassified cluster. Same letters above the boxes indicate insignificant differences between clusters (ANOVA F = 5.69, df (5, 168), p < 0.001).