Urban reserves, as other protected areas, are aimed at preserving species richness but the conservation effort in these protected areas is complicated by a high proportion of alien species. We examined which environmental factors determine the representation of alien species in 48 city reserves of Prague, Czech Republic, distinguishing between archaeophytes, i.e. alien species introduced since the beginning of Neolithic agriculture up to 1500 A.
D., and neophytes, i.e. modern invaders introduced after that date, with the former group separately analysed for endangered archaeophytes (listed as C1 and C2 categories on national red list).