A new insight on the genus Pteridium (Dennstaedtiaceae) in Europe based on a revision in the flora of Slovakia.

Background: The genus Pteridium Gled. ex Scop. was thought to be monotypic with the cosmopolitan species P. aquilinum (L.) Kuhn. for many years. However, morphological variations among these plants in different regions have been noted since the 1940's, leading to the description of new taxa later. Molecular investigations, while not resolving all taxonomical questions within the genus, have highlighted its rich genetic diversity globally, confirming the status of several previously described species and subspecies. This wealth of data has prompted revisions of the Pteridium genus in regional floras, with Northern Eurasia serving as a central arena for such studies in the last 30 years. Recent data suggest that the European flora comprises a single species, P. aquilinum, with two subspecies, P. a. subsp. aquilinum and P. a. subsp. pinetorum (C.N. Page & R.R. Mill) J.A. Thomson. However, their distribution within the continent remains unclear. Therefore, this study aims to elucidate the representation and distribution of Pteridium taxa in Slovakia with an attempt to describe natural ranges of P. aquilinum subspecies based on herbarium materials and citizen science data within Europe for a whole.

Results: It is confirmed that the genus Pteridium is represented by the single species with two mentioned subspecies in the flora of Europe, as well as in the flora of Slovakia. The distribution of these subspecies is mapped in the country. Additionally, we discuss the ranges of these subspecies for a whole, and we evidence the growth of P. aquilinum subsp. pinetorum within the Netherlands, Czechia, Austria, Hungary and Romania for the first time. Also, two new combinations of taxa from the Asian part of Russia are offered.

Conclusion: Our study is a significant contribution in the present knowledge about the distribution and taxonomy of P. aquilinum, however it also shows that many questions concerning this taxon and its infraspecific taxa remain open. Additional field investigations and herbarium processing should be carried out for detailed explorations of biological and ecological peculiarities of the mentioned subspecies, and for the clear understanding of their regional distribution. Such explorations also might become a basis for new syntaxonomic revisions.