A phylum of tracheophyte plants containing the clubmosses (genus Lycopodium) and related genera—including the spikemosses (Selaginella) and quillworts (Isoëtes)—as well as numerous extinct forms, which reached their peak in the Carboniferous period with giant coal-forming tree species. Lycophytes have roots and their stems are covered with numerous small leaves. Reproduction is by means of spores; the sporangia are usually grouped into cones. Phylogenetically, the lycophytes are the sister group to the euphyllophytes, which comprise all other vascular plants.