Description:
<jats:title>Abstract</jats:title><jats:p>The orchid species <jats:italic>Dactylorhiza majalis</jats:italic> is endangered by continuing habitat destruction and fragmentation. This requires more detailed information with respect to its sexual reproduction, which is especially relevant for Germany, where from 10 % to 30 % of the world-wide remaining populations grow. In the present study, we determined both the numbers of growing and flowering individuals per stand with regard to <jats:italic>D. majalis</jats:italic> at 12 localities of Upper Lusatia, Saxony, Germany, during the season 2014. For up to 25 plants per stand, sexual reproduction was assessed by checking over the numbers of blossoms and fruits per inflorescence and by calculating percentages of seed fertilities from embryo-viability stains. Applying pair-wise statistical analyses, we found correlations between two of the above-mentioned traits as well as among the above-cited population-specific reproduction parameters and four out of six Ellenberg’s indicator values, which have been calculated to characterize local site conditions. We furthermore recorded both very poor and enhanced seed fertilities, clustering into two groups which were associated with the Ellenberg’s indicator value thermal continentality. Lower seed fertilities were generally detected in the northern lowlands, whereas <jats:italic>D. majalis</jats:italic> is probably able to compensate the unpleasant environments of the southern highlands by bearing more fertile seeds. Conducting genetic inventories with three nuclear microsatellites, the sampled seed-producing mother plants of both fertility groups differed by the opposite frequency distribution of two prominent genotypes DD and EE at locus ms14. These findings indicate a genetic selection due to adaptation to climatical stresses. Based on the additionally detected aberrant megasporogenesis, we propose that mother plants of homozygous genotype EE and their germ-cells are less affected by both aneuploidy and large deletions on the remaining chromosomes, and we assume that a linkage disequilibrium exists between such advantageous karyotypes and the studied microsatellite locus. Regarding the challenges of global warming, repeated inventories are finally recommended at all 12 stands in order to validate the long-term indicative properties of the discovered findings.</jats:p>