Multiple choice Which of the following is not an example of a short day plant? Chrysanthemum Xanthium Sugarcane Lettuce Reveal answer Fill a bubble to check yourself D Correct answer Explanation Photoperiodism is the ability of plants to measure day length. Lettuce is a long day plant, which flowers after a critical day length is exceeded. Long day plants flower only when photoperiod (day length) is long, that is, summer.