How are lycophyte microphylls different from the leaves of ferns and seed plants?

Lycophyte microphylls are distinguished from the leaves of ferns and seed plants primarily by their simple vascular structure and developmental impact on the plant stem.12

Key differences include:

• Venation: Lycophyte microphylls contain only a single, unbranched vein. In contrast, the leaves of ferns and seed plants typically possess complex, branched venation systems.132
• Stem Anatomy: Because microphylls are simple, their vascular connection to the stem does not disrupt the stem's vascular tissue (stele) configuration and does not create a "leaf gap". Conversely, the complex leaves of ferns and seed plants (often called megaphylls) draw out significant vascular tissue from the stem, which results in the formation of a leaf gap.1
• Evolutionary Origin: While the specific evolutionary history differs, the complex leaves of ferns and seed plants are generally thought to have evolved from branching stem systems, whereas microphylls represent a different evolutionary development of leaf-like appendages.1

Additionally, in lycophytes, sporangia are positioned on the adaxial (upper) surface of the leaf, known as a sporophyll.42