The genus Polypodium includes about 160 species of subcosmopolitan distribution, with maximum diversity in tropical areas. This epiphytic and terrestrial genus is characterized by adnate pinnae, once-pinnate fronds, on a thick, long-creeping and branching rhizome on surface. Big, round, yellow orange sori, without indusium, appear in autumn, on the pinnae underside. Three species and 2 recognized hybrids in European flora : P. interjectum, P. cambricum, P. vulgare, P. x shivasiae and P. x mantoniae. In the Polypodium genus, the species come in many subspecies and varieties, and hundreds of cultivars, especially for P. cambricum. British amateurs and botanists have particularly devoted themselves to identifying, describing and listing, numerous variants and cultivars, since the nineteenth century. To be identify with certainty, European species and hybrids need an thorough observation with a microscope.