Achillea pannonica in the Czech Republic, with taxonomic remarks

Achillea pannonica Scheele is an octoploid species of the A. millefolium group. Based on herbarium and field studies, a taxonomic and phytogeographic account of this taxon is provided in the Central European part of its range. The synonymy of A. pannonica includes A. seidlii J. Presl et C. Presl, A. millefolium var. lanata W. D. J. Koch, and Achillea millefolium f. contracta Schltdl. Achillea pannonica is a clearly delimited species: no variation deserving taxonomic recognition was observed in Central European plants. Morphological differences between A. setacea Waldst. et Kit. and A. pannonica are summarised in a table. Achillea pannonica is classified as a subtemperate to submeridional subcontinental European species or as a Pontic element with overlaps to the Balkans and westernmost Anatolia. Its range in the Czech Republic is divided into two parts including northern and central Bohemia, and southern and central Moravia, all warm to moderately warm and dry to moderately dry regions. Two distribution maps based on more than 1280 specimens revised are presented. The distribution pattern of A. pannonica in the Czech Republic which coincides well with the distribution of thermophilous oak woods of the order Quercetalia pubescenti-petraeae can be compared to that of Anagallis foemina, Cerasus fruticosa, Dictamnus albus, and Lavatera thuringiaca. It is probably a relict of the more continuous range which may have developed in the early Holocene. Achillea pannonica is a heliophilous to heliosciophilous species of dry grasslands, fringe communities, thermophilous oak forests and some thermophilous (sub)ruderal communities. It grows on several types of rock and often prefers calcareous substrata such as limestone and loess. At several sites, it was observed to occur together with other yarrows. Hybridization with A. millefolium s. str. sometimes occur, and the new nothospecies, A. ×incognita, is formally described; however, its reliable recognition requires chromosome counts.