Wouldn’t it be beyond-beautiful if we had a clock which did not tell time by mundane numbers and needles, but by a particular flower blooming? Imagine if you peeped out of the window and you could look at this clock, and tell if it was 12 noon, or 1 pm or 2 pm by the flower that was blooming!
This was the kind of clock that Carl Linnaeus dreamed of. Linnaeus’s flower clock or Horologica Floræ is a garden-plan thought up by Linnaeus that would take advantage of plants that open or close their flowers at particular times of the day, to accurately indicate the time.
As most of us would remember from school-biology, Linnaeus was the Swedish naturalist who laid down the principles for defining genera and species of organisms, and created a uniform system for naming them (the binomial nomenclature). His book, Systema Naturae (The System of Nature) consisted of only 11 pages but laid the foundations of taxonomy. It presented a hierarchical classification or taxonomy, of the three kingdoms of nature: stones, plants, and animals. Each kingdom was subdivided into classes, orders, genera, species, and varieties. All modern classification systems in biology have their roots in the Linnaean classification system which is based on similarities—for instance, Linnaeus grouped together organisms that shared obvious physical traits, such as number of legs or shape of leaves.
The Linnaean system of classification consists of a hierarchy of groupings, called taxa (singular, taxon). Taxa range from the kingdom to the species. The kingdom is the largest and most inclusive grouping. It consists of organisms that share just a few basic similarities. Examples are the plant and animal kingdoms. Then come the phylum, then the class, order, family, genus, and finally the species–the smallest and most exclusive grouping. It consists of organisms that are similar enough to produce fertile offspring together.
Linnaeus greatest contribution to science was his method of naming species. This method, called binomial nomenclature, gives each species a unique, two-word Latin name consisting of the genus name and the species name. An example is Homo sapiens, the two-word Latin name for humans, literally meaning “wise human.”
But if Linnaeus saw order in the natural world around him, he saw beauty too. In around 1748 he started thinking about the flower-clock. It builds on the fact that there are species of plants that open or close their flowers at set times of day. In his publication Philosophia Botanica, he gives 46 examples of flowering plants that are open during particular parts of the day. He brought together 43 of these under the heading Horologium Florae, or Floral Clock, arranging them in a time sequence from 3 am to 8 pm. The time at which each flower opens and closes is given in whole and half hours.
To give you a glimpse, here are a few rows from Linnaeus’ table:
| Botanical name | Common name | Opening time | Closing time |
| Tragopogon pratensis | Goat’s-Beard | 3 a.m. | – |
| Cichorium intybus L. | Chicory | 4–5 a.m. | – |
| Reichardia tingitana (L.) Roth | False Sow thistle | by 6 a.m. | 10 a.m. |
| Taraxacum officinale Weber | Dandelion | 5 a.m. | 8–9 a.m. |
| Crepis alpina L. | Hawk’s beard | 5 a.m. | 11 a.m. |
| Hieracium umbellatum L. | Hawkweed | 6 a.m. | 5 p.m. |
Though Linnaeus worked for years on this, the observations and hence selection and organization of flowers were not complete. Linnaueus’ son Carl the Younger was given the task for completing the table so that the clock could be built. Unfortunately, Linnaeus the Younger’s floral clock was never completed, and his observations on the opening and closing of flower have not been found among his surviving papers.
Alas, no one has actually built such a clock, and it is not even clear that it is possible. There are many practical issues to overcome. For instance, it would only function for part of the year since plants don’t flower through the year; the time shown would be indicative at best since blooming times are in a range and would vary with specifics like weather and other atmospheric conditions; many of the plants that Linnaeus observed and selected were wildflowers from Sweden and may not be found in other places, or would behave differently in other places. And then, the clock may not work at all in some seasons, if there are not enough flowers which bloom then.
Well, in this digital age, there are some ingenious people who have created an app based on the idea. They have selected 24 flowers, one for each hour that would normally flower at that time of the day or night. Floræ – Linnaeus’ flower clock app is free on appstore for Apple and iPhone.
So maybe we have make do with that, till some genious actually builds the Horologica Floræ to blow our minds!
–Meena
https://www.countrylife.co.uk/nature/curious-questions-what-is-linnaeuss-flower-clock-259032
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