Differentiation of Dryopteris expansa and its hybrid D. xambroseae and revision of their distribution in the Czech Republic

The distribution of Dryopteris expansa and D. ×ambroseae (D. dilatata × D. expansa) was studied in the Czech Republic. Collections from 22 Czech public herbaria were revised and a total of 479 specimens were examined. The hybrid D. ×ambroseae often occurs together with D. expansa. In the Czech Republic, the greatest frequency of D. expansa was recorded at locations with a high air moisture (e.g. mountain areas and foothills with beech and spruce forests). At lower altitudes, the species occurs in deep valleys with alder forests along streams and rivers or around springs. Dryopteris expansa is very common in gorges and canyons in sandstone areas in the Czech Cretaceous Basin (Česká křídová pánev) and scattered on cold screes of the hills of České středohoří Mts. Lowland occurrences were rarely detected in alluvial forests. Dryopteris expansa occurs at altitudes from 200 to 1420 m and most frequently at altitudes from 500 to 700 m. A short summary of the taxonomy and hybridisation in the D. carthusiana group is given. An identification key, distribution maps and notes to the differentiation, hybridisation and habitat preferences are presented as well.