A fern is a member of a group of roughly 12,000 species of vascular plants that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular (i.e. having water-conducting vessels). They have stems and leaves, like other vascular plants. Most ferns have what are called fiddleheads that expand into fronds, which are each delicately divided.
Leptosporangiate ferns (sometimes called "true ferns") are by far the largest group, but ferns as defined here (ferns sensu lato) include horsetails, whisk ferns, marattioid ferns, and ophioglossoid ferns. This group may be referred to as monilophytes. The term pteridophyte traditionally refers to ferns plus a few other seedless vascular plants (see the classification section below), although some recent authors have used the term to refer strictly to the monilophytes.