Ferns: Seedless nonflowering plants of the class Filicinae. They reproduce by spores that appear as dots on the underside of feathery fronds. In earlier classifications the Pteridophyta included the club mosses, horsetails, ferns, and various fossil groups. In more recent classifications, pteridophytes and spermatophytes (seed-bearing plants) are classified in the Subkingdom Tracheobionta (also known as Tracheophyta).Pteridium: A plant genus of the family DENNSTAEDTIACEAE. Members contain ptaquiloside, braxin A1, and braxin B. The name is similar to brake fern (PTERIS).Pteridaceae: A plant family of the order Polypodiales, class Filicopsida, division Pteridophyta (FERNS).Pteris: A plant genus of the family PTERIDACEAE. Members contain entkaurane DITERPENES. The name is similar to bracken fern (PTERIDIUM).Germ Cells, Plant: The reproductive cells of plants.Marsileaceae: A plant family of the order Hydropteridales, class Filicopsida, division PTERIDOPHYTA. They are aquatic ferns with quatrifoliate leaves resembling four leaf clover, creeping rhizome, and bean shaped sporocarps.Polypodiaceae: The fern plant family of the order Polypodiales, class Filicopsida, division Pteridophyta, subkingdom Tracheobionta.Adiantum: A plant genus of the family Pteridaceae. Members contain TRITERPENES. Some species in this genus are called maidenhair fern which is also a common name occasionally used for Lygodium (FERNS) and POLYPODIUM.Polypodium: A plant genus of the family POLYPODIACEAE. Members contain polypodoside.Spores: The reproductive elements of lower organisms, such as BACTERIA; FUNGI; and cryptogamic plants.Dryopteridaceae: The wood fern plant family of the order Polypodiales, class Filicopsida, division Pteridophyta.Dryopteris: A plant genus of the family DRYOPTERIDACEAE. Members contain aspidin and filicic acid.