Linnaeus' Flower Clock.

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linneo flower clockLinnaeus' 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.
He may never have planted such a garden, but the idea was attempted by several botanical gardens in the early 19th century, with mixed success.

linnean-flower-colckMany plants exhibit a strong circadian rhythm, and a few have been observed to open at quite a regular time, but the accuracy of such a clock is diminished because flowering time is affected by weather and seasonal effects.

The flowering times recorded by Linnaeus are also subject to differences in daylight due to latitude: his measurements are based on flowering times in Uppsala, where he taught and had received his university education.

The plants suggested for use by Linnaeus are given in a table below, ordered by recorded time. A "-" signifies that data are missing.
6 AM Spotted Cat’s-ear opens
7 AM African Marigold opens
8 AM Mouse-ear Hawkweed opens
9 AM Prickly Sow-thistle closes
10 AM Nippleworth closes

11 AM Star of Bethlehem opens
Noon Passion-flower opens
1 PM Childing Pink closes
2 PM Scarlet Pimpernell closes
3 PM Hawkbit closes
4 PM Small Bindweed closes
5 PM Water-lily closes

6 PM Evening Primrose opens

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