Rice spikelet development and fertility improving rice grain yield is a major focus of breeders around the world. The spikelet is the basal unit of the rice panicle and its correct development is crucial for reproductive success. We will report on the role of three ERECTA/ERECTA-like leucine-rich receptor-like kinases in rice spikelet formation. The Arabidopsis ERECTA gene family as a whole has been shown to regulate floral meristem function, inflorescence architecture and organ shape, but the role of its individual members remains unknown. Furthermore, ERECTA gene function has not been investigated at all in any other type of inflorescences. Our results reveal the synergistic roles of the three rice ERECTA-like genes in the regulation of floral meristem determinacy and floral organ identity, through partial redundancy as well as specificity among family members. Furthermore, we identify environmental factors that strongly modulate the function of rice ERECTA homologs in inflorescence development and fertility, with implications for the potential of these genes as tools for genetic improvement of floral development in rice and its adaption to environmental change.