The daylength varies with the time of the year and can thus be used by plants—and other organisms—to react photoperiodically in developmental steps and morphological features such as cyst formation, germination of zygospores and cell division in certain algae, succulence of stems and leaves, formation of storage organs, and flower induction. The functioning and molecular bases of circadian clocks of plants are mentioned and shown how they are entrained to the day, and whether they are involved in photoperiodic timing. Seasonal aspects for various crops and the evolution of photoperiodism are briefly touched upon.
Engelmann, W. (2015). Photoperiodism: The calendar of plants. In Rhythms in Plants: Dynamic Responses in a Dynamic Environment (pp. 191–229). Springer International Publishing. https://doi.org/10.1007/978-3-319-20517-5_8