This suggests that the mechanisms for regulating determinacy and indeterminacy were present in the common ancestor of vascular plants and were recruited independently to control leaf initiation. By contrast, a mechanism involving Class III HD-Zip transcription factors that pattern stem vasculature was co-opted for the adaxial/abaxial patterning of leaves in seed plants but not in lycophytes [60], reflecting the independent origin of microphylls and seed plant megaphylls.