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LEAFY plant-specific transcription factors, which are key regulators of flower meristem identity and floral patterning, also contribute to meristem activity. Notably, in some legumes, <i>LFY</i> orthologs such as <i>Medicago truncatula SINGLE LEAFLET</i> (<i>SGL1</i>) are essential in maintaining an undifferentiated and proliferating fate required for leaflet formation. This function contrasts with most other species, in which leaf dissection depends on the reactivation of <i>KNOTTED</i>-<i>like</i> class I homeobox genes (<i>KNOXI</i>). <i>KNOXI</i> and <i>SGL1</i> genes appear to induce leaf complexity through conserved downstream genes such as the meristematic and boundary <i>CUP-SHAPED COTYLEDON</i> genes. Here, we compare in <i>M. truncatula</i> the function of <i>SGL1</i> with that of the <i>Arabidopsis thaliana KNOXI</i> gene, <i>SHOOT MERISTEMLESS</i> (<i>AtSTM)</i>. Our data show that <i>AtSTM</i> can substitute for <i>SGL1</i> to form complex leaves when ectopically expressed in <i>M. truncatula</i>. The shared function between <i>AtSTM</i> and <i>SGL1</i> extended to the major contribution of <i>SGL1</i> during floral development as ectopic <i>AtSTM</i> expression could promote floral organ identity gene expression in <i>sgl1</i> flowers and restore sepal shape and petal formation. Together, our work reveals a function for <i>AtSTM</i> in floral organ identity and a higher level of interchangeability between meristematic and floral identity functions for the AtSTM and SGL1 transcription factors than previously thought.