Achillea pratensis - a recently recognized species of the Czech flora

Milfoils (Achillea millefolium agg.) of the Czech Republic were studied in the field as well as in most of the Czech herbaria. Achillea pratensis Saukel et Länger, recently described from Austria, was found to be common in the Czech Republic. Its occurrence was confirmed by chromosome counts (2n = 36) in 74 plants from 26 localities, and more than 240 herbarium specimens of this species were revised. Seasonal variation of A. pratensis was analysed using canonical discriminant analysis. The first generation (spring) and second generation (summer) shoots proved to be morphologically different (they can be separated mainly by number of nodes, shoot height, leaf width, and bract length). Thus, the description of the species provided by Saukel & Länger had to be modified to include spring shoots. Morphological and taxonomic delimitations from other tetraploids (A. collina Rchb.) have not yet been satisfactorily defined. Also, taxonomic relationships to A. tenuis Schur described from Transylvania as well as to A. submillefolium Klokov et Krytzka described recently from the Ukraine remain to be clarified. The phytosociological affinity of A. pratensis in the Czech Republic is documented by 18 relevés. The species is confined mainly to mesophilic meadows of the alliance Arrhenatherion, to grasslands such as street and garden lawns which can be classified only to the order Arrhenatheretalia as well as to continental floodplain meadows of the alliance Cnidion venosi. Sympatric occurrence of several Achillea taxa of different ploidy levels was observed at several localities and the presence of natural hybrids (A. millefolium × A. pratensis, 2n = 45) was indicated at two sites by chromosome counts.