Diversity of the genus Riccia (Marchantiophyta) and molecular methods of taxonomical study of liverworts

The main objective of this study is to introduce the genus Riccia. The first fossil discoveries of this genus date back to the Early Pleistocene. It has been known from literature since the 17th century. From this time forward it gets more attention. This genus has a cosmopolitan distribution across all of the world. It is capable of surviving extreme conditions. Also it adapts to new conditions quite easily. Representatives of genus Riccia have a very wide range of morphological variations. Therefore to this day there are still issues with a properly species determination. In the Czech Republic there are 13 species and 3 of it are easily interchangeable. Mainly, I focus on R.fluitans, which its a typical habitat is a water level. If R.fluitans lacks the aquatic environment, then It can look like terrestrial R.rhenana. The next chapter is about a description of basic metods in molecular studies on Marchantiophyta. Molecular data have changed significantly a view on the Marchantiophyta taxonomy. Until recently the taxonomy was dependent on morphological similarities. But modern metods don't always guarantee the correctness. Therefore it is recommended to combine molecular results with morphological features. Keywords: Riccia, diversity, variability, molecular study, Marchantiophyt