Internal biological clocks in plants that regulate daily cycles of physiological processes, typically following a roughly 24-hour pattern. These rhythms control activities like leaf movement, flower opening, and metabolic processes even in constant environmental conditions.
From Latin 'circa' meaning 'about' and 'dies' meaning 'day,' literally 'about a day.' The term was coined in the 1950s by chronobiologist Franz Halberg, though the phenomenon in plants was observed much earlier by astronomers noting daily leaf movements.
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