A florigen paralog is required for short-day vernalization in a pooid grass.

Perception of seasonal cues is critical for reproductive success in many plants. Exposure to winter cold is a cue that can confer competence to flower in the spring via a process known as vernalization. In certain grasses, exposure to short days is another winter cue that can lead to a vernalized state. In , we find that natural variation for the ability of short days to confer competence to flower is due to allelic variation of the () paralog (). An active allele is required for the acquisition of floral competence, demonstrating a novel role for a member of the family of genes. Loss of the short-day vernalization response appears to have arisen once in and spread through diverse lineages indicating that this loss has adaptive value, perhaps by delaying spring flowering until the danger of cold damage to flowers has subsided.