A fern is any one of a group of about 12,000 species of plants. Unlike mosses, they have xylem and phloem (making them vascular plants). They have stems, leaves, and roots like other vascular plants. Ferns do not have either seeds or flowers (they reproduce via spores).
By far the largest group of ferns are the leptosporangiate ferns, but ferns as defined here (also called monilophytes) include horsetails, whisk ferns, marattioid ferns, and ophioglossoid ferns. The term pteridophyte also refers to ferns (and possibly other seedless vascular plants). A pteridologist is a specialist in the study of ferns and lycophytes.
Ferns first appear in the fossil record 360 million years ago in the Carboniferous but many of the current families and species did not appear until roughly 145 million years ago in the late Cretaceous (after flowering plants came to dominate many environments).
Ferns are not of major economic importance, but some are grown or gathered for food, as ornamental plants, or for remediating contaminated soils. Some are significant weeds. They also featured in mythology, medicine, and art.