any of the spore-bearing plants, also known as vascular cryptogams, in the divisions Pteridophyta and Lycophyta. The name pteridophyte is derived from Greek words meaning “feather plant.” It is used commonly and informally to denote the ferns (fern) and fern allies. Views on the classification of the spore-bearing vascular plants have been refined as data from molecular markers have clarified relationships between the more primitive groups. Molecular and structural studies indicate that the club mosses and their relatives are ancestral to all other modern groups of vascular plants. In contrast, the ferns—including the horsetails, whisk ferns, and other relatively primitive groups—appear to represent a cohesive evolutionary group that is sister to the seed plants. This expanded concept of ferns is sometimes called by the informal name monilophytes.