Karyological, morphological and ecological differentiation of Sesleria caerulea and S. tatrae in the Western Carpathians and adjacent regions.

The tetraploid (2n = 4x = 28) Sesleria caerulea and octoploid (2n = 8x = 56) S. tatrae are closely related species with very similar morphology. These species can tolerate a wide range of ecological conditions, and in areas where the two co-occur, individual plants are often hardly distinguishable and assumed to be products of hybridization. Consequently, the ecological requirements of each species and the evolutionary relationship between the two species remain unknown. The aim of this study is to determine the karyological, morphological and ecological differentiation between the two species. A total of 877 S. caerula and S. tatrae plants from 68 populations in the Western Carpathians, Alps and Sudetes mountain ranges were analysed for DNA ploidy level and subjected to morphometric examination. Moreover, phytosociological relevés for each location and Ellenberg’s indicator values were used as supplementary environmental variables for interpreting the results from an ecological point of view. All individuals of S. caerulea were tetraploid and all those of S. tatrae octoploid. There were no intermediate ploidy levels, which would indicate hybrids between the two species. Morphometric analyses of 28 morphological characters revealed that eight were significantly different in these two species. Of these, density of hairs between the veins on the lemma, and length of lemma, glume and palea were the most reliable diagnostic characters. Morphological dissimilarities, however, were found only at the population level and were not always useful in identification of individual plants. Important differences between the two species were also found in ecological requirements. Detected ecological differences were mostly associated with altitude, moisture, temperature, light intensity and nutrient levels, in terms of which Sesleria caerulea was most tolerant. Conversely, S. tatrae grew under a more narrow range of conditions, occurred at high altitudes and preferred high humidity, high light intensities and nutrient-rich soils. The name Sesleria tatrae is typified.