leaf (Q1490)

(1.) A principal, vegetative shoot organ borne laterally from a stem node; its vascular tissues, if any, continuous with those of the stem; undergoing no significant secondary growth; usually more or less bilaterally symmetrical; comprising a distal, usually laminar blade and/or a proximal stalk (petiole) or sheath; usually a primary site of photosynthesis. (2.) A small, lateral, leaf-like enation that, evolutionarily, is not a true leaf, i.e., whose vasculature, if any, consists of only a single median strand not ontogenetically integral with the vasculature of the bearing stem and not associated with leaf gaps in the stele of the stem; in Psilotophyta, Lycopodiophyta, Equisetophyta.