Floral Clock (redirected from Petal Time Clock)

Floral Clock 

a group of herbaceous plants set out on a small area whose flowers open and close at definite times of the day (with accuracy of ½ to 1 hour). Thus, the floral clock makes it possible to determine the time with approximate accuracy. The first floral clock was laid out by the Swedish naturalist C. Linnaeus at Uppsala in the 1720’s. It started between 3:00 and 5:00 A.M., when the flowers of Trapogon pratensis opened, and ended at midnight, when the flowers of Celenicereus grandiflorus opened. The opening and closing of the flowers occur on clear and sunny days; in overcast or rainy weather these phenomena are almost imperceptible or are greatly delayed. The opening and closing of flowers depend on many other conditions, including geographic location and the time of sunrise and sunset. For this reason, different flowers must be used in different localities; laying out a floral clock in a particular region requires preliminary observations over a period of many years.