What is "microphyll"

n. 1 (context botany English) A leaf having a single unbranched vein, or a structure that is derived from such a leaf. 2 (context botany English) A very small leaf

In plant anatomy and evolution a microphyll is a type of plant leaf with one single, unbranched leaf vein. Plants with microphyll leaves occur early in the fossil record, and few such plants exist today. In the classical concept of a microphyll, the leaf vein emerges from the protostele without leaving a leaf gap. Leaf gaps are small areas above the node of some leaves where there is no vascular tissue, as it has all been diverted to the leaf. Megaphylls, in contrast, have multiple veins within the leaf and leaf gaps above them in the stem.