Microphylls are defined as leaves having
Microphyll evolution follows enation theory explaining small leaf origin as novel lateral outgrowths from stem later vascularized. Anatomically microphyll contains one central, unbranched vascular strand originating from protostele without disrupting stele, hence no leaf gap or parenchymatous breaks above trace. Megaphylls contain multiple veins derived from branched telomes. Single strand criterion differentiates lycophylls of Lycopodiaceae and Selaginellaceae from true euphylls of ferns. Absence of vascular tissue or phloem-only configuration contradicts definition of functional microphyll w
Ref: Gifford & Foster Comparative Morphology; Eames Morphology Vascular Plants, microphyll