Controls the morphogenesis of lateral organs. Functions in lateral organ shape and is sufficient to induce proliferation and growth of lateral organ tissue. Is necessary and sufficient for bract formation, but its expression is excluded from the cryptic bract, which could be a cause of bractless flowers in Arabidopsis. Participates with FIL and YAB3 in regulating valve margin development. Functions with JGL to define stamen and carpel shape. Functions with AS1 and AS2 in the sepal and petal primordia to repress boundary-specifying genes for normal development of the organs. Interacts with GATA18/HAN. Expressed in the emerging leaf, sepal, petal, stamen and carpel primordia (PubMed:26390296). Not expressed in the apical shoot meristem (SAM). Stimulated by GATA18/HAN. Lateral organs with serrated margins. Irregular shape of floral organs. The double mutant han-2 jag-3 exhibits reduced petal numbers, more serrated sepals and narrower petals (PubMed:26390296). Plants overexpressing JAG form bract-like organs on the inflorescence.