euphyllophyte

Euphyllophyte is a clade of vascular land plants that includes all living ferns and seed plants, together with their extinct relatives. The defining feature is the possession of megaphyllous leaves, leaves with a branched vascular network, as opposed to the microphyll leaves typical of lycophytes. Euphyllophytes also display more complex leaf and stem vascular organization and a tendency toward more elaborate growth forms in many lineages.

Phylogenetically, euphyllophytes are part of the tracheophytes (vascular plants) and are commonly regarded as sister to the lycophyte lineage. The origin of megaphyllous leaves is placed in the ancestor of the euphyllophytes during the late Silurian to early Devonian, setting the stage for later diversification. The clade comprises two major living lineages: Monilophyta (ferns, horsetails, and their relatives) and Spermatophyta (seed plants, including gymnosperms and angiosperms). The seed plant lineage gave rise to the vast majority of land plants in later eras, while monilophytes include many tree ferns and various herbaceous forms.

Fossil evidence supports a long history for euphyllophytes, with megaphyllous leaves becoming widespread in early to middle Paleozoic ecosystems. The evolution of seeds, pollen, and extensive vascular systems within the spermatophytes contributed to widespread terrestrial diversification, while ferns and their relatives remained important components of many habitats.

In modern classifications, Euphyllophyta is treated as a major clade within the vascular plants (Tracheophyta), distinct from the lycophyte lineage. The term highlights the key evolutionary innovation of true leaves and marks a major split in the early evolution of land plants.