The length of the day and night required for the initiation of flowering is called photoperiod. Depending upon the length of photoperiod, Garner and Allard classified plants into three groups. They are Short day plants, Long day plants and Day neutral plants.
A plant which requires less than 12 hours of day length for the imitation of flowering is called a short day plant.
Example of Short Day Plants:
 
- Rice (Oryza sativa)
- Coffee(Coffee arabica)
- Tobacco(Nicotiana tobacum)
- Soyabean(Glycine max)
- Chrysanthemum
- Cosmos(Cosmos sulphureus)
- Cocklebur (Xanthium pennsylvanicum)
The short day plants require nights of more than 12 hours length. Hence short day plants are also called long light plants.
