What is the assumed phylogenetic origin of leaves?

Question

What is the assumed phylogenetic origin of leaves?

Answer 1

Vascular plants possess leaves with highly branched vascular systems. These types of leaves are known as megaphylls. They first appear in the fossil record about 370 million years ago. It is thought that leaves originated in primitive vascular plants that lived at that time. One model proposes that small thin branches that grew closely together flattened and developed webbed photosynthetic tissue between them. This kind of developmental change has been observed in other living things, such as the evolution of webbing between the digits in aquatic birds and mammals, and in flying and gliding mammals as well.