A division of the plant kingdom, commonly called the ferns, which is widely distributed throughout the world but is most abundant and varied in moist, tropical regions. The Polypodiophyta are sometimes treated as a class Polypodiopsida of a broadly defined division Tracheophyta (vascular plants). The group consists of five living orders (Ophioglossales, Marattiales, Polypodiales, Marsileales, and Salviniales), plus several orders represented only by Paleozoic fossils. The vast majority of the nearly 10,000 species belong to the single order Polypodiales, sometimes also called Filicales.