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Circadian rhythms, endogenous rhythms with periods of approximately 24 h, are widespread in nature. Although plants have provided many examples of rhythmic outputs and our understanding of photoreceptors of circadian input pathways is well advanced, studies with plants have lagged in the identification of components of the central circadian oscillator. Nonetheless, genetic and molecular biological studies, primarily in Arabidopsis, have begun to identify the components of plant circadian systems at an accelerating pace. There also is accumulating evidence that plants and other organisms house multiple circadian clocks both in different tissues and, quite probably, within individual cells, providing unanticipated complexity in circadian systems.
C. Robertson McClung (Fri,) studied this question.