Influence of environmental and intrinsic factors on the flowering success and petal morphology of Pulsatilla patens and the hybrid Pulsatilla patens × vernalis in Finland

Combatting the biodiversity crisis through management and conservation requires specific information on the basic biology of species in decline. The Eastern pasqueflower, Pulsatilla patens, has declined drastically in Europe and in Finland is currently confined to a few locations. The aim of this study was to assess which factors influence fitness-related traits of P. patens and a hybrid species P. patens × vernalis. To this end we recorded morphological and environmental variables over a three-year period on individually marked P. patens and hybrid individuals in eight locations in southern Finland. The number of flowers decreased significantly each year for P. patens while for the hybrid there was first an increase and then decrease. Hybrids produced on average more flowers than P. patens individuals and the share of flowering individuals was higher in hybrids than in pure pasqueflowers. In general, for both P. patens and the hybrid, larger plant diameter, cooler and drier conditions and greater canopy openness positively affected number of flowers and flowering probability, although some species-specific differences were evident with a preference for greater canopy density for P. patens than the hybrid. Although our results support current conservation practices of creating more open environments to benefit flowering of P. patens, there also appears to be a limit to the amount of direct sunlight P. patens will tolerate, thus warranting caution. At present, the hybrid does not appear to be of immediate concern to the endangered P. patens, although continued monitoring of the populations is recommended.