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Initiation and growth of leaf blades in higher plants is linked to the development of adaxial/abaxial polarity in leaf primordia. This process is dependent on the expression of PHANTASTICA (PHAN), a MYB transcription factor involved in negative regulation of KNOX gene expression in lateral organ primordia. McHale and Koning (pages 1251-1262) present a novel view of PHAN function in Nicotiana sylvestris (NsPHAN), pointing to distinctly different roles in development of juvenile and adult leaves. The authors propose that NsPHAN, acting through KNOX repression, maintains gibberellic acid-dependent patterns of cell proliferation critical to palisade formation in juvenile leaf blades. In adult leaves, they suggest that KNOX repression blocks the encroachment of radical patterning from internodes into leaf petioles of adult leaves. The cover image shows an anti-sense NsPHAN transgenic plant in the adult vegetative phase.