Final answer:
The Christmas cactus blooms during the season due to shorter daylight hours and cooler temperatures, indicating to the short-day plant that it is time to flower.
Step-by-step explanation:
Schlumbergera bridgesii, commonly known as Christmas cactus, is a popular houseplant that blooms during the Christmas season. Despite not having the ability to read a calendar, this plant senses the time of year through environmental cues. The blooming of the Christmas cactus is triggered by a combination of cooler temperatures and longer nights as winter approaches. This is because the Christmas cactus is a short-day plant, meaning it initiates flowering when the daylight hours are fewer than a certain threshold, usually less than 12 hours per day. Additionally, the plant employs the CAM photosynthetic pathway, common in many succulents, which is advantageous for water conservation.