enation theory The theory that accounts for the origin of the fern leaf by suggesting that it arose from the development of simple outgrowths (enations). Any such theory has to account for the large, branching fronds of a fern with branching veins (a ‘megaphyll’) and also for the small leaves (‘microphylls’) with a single median vein.

enation theory The theory that accounts for the origin of the fern leaf by suggesting that it arose from the development of simple outgrowths (enations). Any such theory has to account for the large, branching fronds of a fern with branching veins (a ‘megaphyll’) and also for small leaves (‘microphylls’) with a single median vein.