Conyza bonariensis (L.) Cronquist and C. triloba Decne. are reported as new alien species to the Czech Republic and Europe, respectively. Conyza bonariensis was collected in 1964 and 1965 in two localities in N Bohemia; the specimens are deposited in PRA. In both cases, the plants were introduced with cotton and occurred in areas of textile factories. Conyza triloba was collected once at the pond in the village of Černivsko in S Bohemia in 1971; the specimen is deposited in PR. The mode of introduction is unknown.