Linnaeus’ Floral clock ~ Linnaeus observed over a number of years that certain plants constantly opened and closed their flowers at particular times of the day, these times varying from species to species. Hence one could deduce the approximate time of day according to which species had opened or closed their flowers. Arranged in sequence of flowering over the day they constituted a kind of floral clock or horologium florae, as Linnaeus called it in his Philosophia Botanica, 1751.
Linnaeus' flower clock was a garden plan hypothesized by Carolus Linnaeus that would take advantage of several plants that open or close their flowers at particular times of the day to accurately predict the time. He called it specifically the Horologium Florae (lit. "flower clock"), and proposed the concept in the 1751 publication Philosophia Botanica.