Plants are generally sessile photosynthetic autotrophs; they depend on light for their existence and cannot move to escape challenging environmental conditions. This means that the lives of plants are intimately linked to daily fluctuations in environmental conditions caused by the rotation of the Earth on its axis. As a result, circadian regulation has an incredibly pervasive influence upon plant physiology, metabolism and development. For example, around 30% of the transcriptome of the model plant Arabidopsis thaliana is circadian regulated. In plants, the circadian clock influences processes of crucial importance such as photosynthesis, opening of the stomatal pores that allow gas exchange with the atmosphere, plant growth rates and organ position. It also contributes to the seasonal regulation of flowering. Taken together, this means that the circadian clock influences plant traits that are crucial to agricultural food production.