Class Marattiopsida is a group of ferns containing a single order, Marattiales, and family, Marattiaceae. Class Marattiopsida diverged from other ferns very early in their evolutionary history and are quite different from many plants familiar to people in temperate zones. Many of them have massive, fleshy rootstocks and the largest known fronds of any fern. The Marattiaceae is one of two groups of ferns traditionally known as eusporangiate fern, meaning that the sporangium is formed from a group of cells vs the leptosporangium in which there is a single initial cell. There have long been four traditional extant genera (Angiopteris, Christensenia, Danaea and Marattia), but recent genetic/cladistic analysis has determined the genus Marattia to be paraphyletic, and the genus has been split into three genera, the two new ones being Eupodium and Ptisana. This fern group has a long fossil history with many extinct taxa (Psaronius, Asterotheca, Scolecopteris, Eoangiopteris, Qasimia, Marantoidea, Danaeites, Marattiopsis, etc.).