Photoperiodism
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Also known as: daylength response
Photoperiodism is the physiological response of plants to the duration of light and darkness in a 24-hour cycle. Short-day plants (chrysanthemums, poinsettias) flower when nights exceed a critical length. Long-day plants (spinach, lettuce) flower when days exceed a critical length. Day-neutral plants (tomatoes, corn) flower regardless of photoperiod. This response involves the photoreceptor phytochrome and the flowering hormone florigen.
Etymology
From Greek phos (light) + periodos (cycle, going around)
Example
“Commercial poinsettia growers exploit photoperiodism by controlling light exposure to force blooms for the holiday season.”