Types of Photoperiodic Plants.
a) Long-day plants
A long-day plant flowers when the day length exceeds their critical photoperiod. These plants typically flower in the northern hemisphere during late spring or early summer as days are getting longer. Some long-day obligate plants are:
- Carnation (Dianthus)
- Henbane (Hyoscyamus)
- Oat (Avena)
Some long-day facultative plants are:
- Pea (Pisum sativum)
- Barley (Hordeum vulgare)
- Lettuce (Lactuca sativa)
- Wheat (Triticum aestivum, spring wheat cultivars)
—prepared by: Subodh Khanal
- Turnip (Brassica rapa)
b) Short-day plant
Short-day plants flower when the day lengths are less than their critical photoperiod. They cannot flower under long days or if a pulse of artificial light is shone on the plant for several minutes during the middle of the night; they require a consolidated period of darkness before floral development can begin. Natural nighttime light, such as moonlight or lightning, is not of sufficient brightness or duration to interrupt flowering.
Some short-day obligate plants are:
- Chrysanthemum
- Coffee
- Poinsettia
c) Day-neutral plants
Day-neutral plants, such as cucumbers, roses, and tomatoes, do not initiate flowering based on photoperiodism at all; they flower regardless of the night length. They may initiate flowering after attaining a certain overall developmental stage or age, or in response to alternative environmental stimuli, such as vernalization (a period of low temperature), rather than in response to photoperiod.
