Polypodiopsida (ferns)

The class Polypodiopsida encompasses both wholly fossil and also living representatives, many of which have a long fossil history. The general features of the class can be summarized as follows:

The living Polypodiopsida fall into six orders, namely the Marattiales, Ophioglossales, Psilotales, Osmundales, Polypodiales and Hydropteridales, referred to collectively as ferns. Of these, the first three orders are eusporangiate (p. 151), while the Polypodiales, and the Salviniales and Marsileales (p. 212) of the now validated Hydropteridales (p. 216), are leptosporangiate (p. 190). The Osmundales have in general leptosporangiate characteristics, but the sporangia develop in a manner recalling that of eusporangiate sporangia. The ferns are an important element of the world's flora, numbering about 10000 species and being particularly conspicuous in warm humid regions. They show the greatest range of growth forms amongst the vascular archegoniates. Although largely herbaceous, a number of ferns of the tropics and subtropics (mostly belonging to the family Cyatheaceae) achieve the form and stature of simple trees.