In plant cytokinesis, SNARE complexes mediate vesicle fusion for partitioning membrane formation. Park et al. show that evolutionarily ancient Qa-SNARE SYP132 functionally overlaps with flowering plant- and cytokinesis-specific Qa-SNARE KNOLLE. KNOLLE acquisition may have been due to high demand for membrane-fusion capacity during endosperm cellularization in flowering plants