Appearing in the Devonian, ferns radiated into diverse species that coexisted with tree lycopods and horsetails in the great Carboniferous forests. Fern leaves are generally much larger than those of lycopods and probably evolved in a different way. Lycopods have microphylls , small leaves that probably evolved as emergences from the stem that contained a single strand of vascular tissue. Ferns have probably evolved from webbing formed between separate branches growing megaphylls , leaves with a branched system of veins. Megaphylls close together.
Most ferns have fronds , compound leaves that are divided into several leaflets.
The emerging frond is coiled into a fiddlehead that unfurls as it grows. The spore is the dispersal stage. The free-living gametophyte is small and fragile, requiring a moist habitat. Water is necessary for fertilization, since flagellated sperm cells must swim from the antheridium to the archegonium, where fertilization takes place. The sporophyte embryo develops protected within the archegonium.