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Linnaeus' flower clock

Linnaeus' flower clock

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. 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. Many 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 is missing.

Botanical name Common name Opening time Closing time
Tragopogon pratensis Goat's-Beard 3 a.m. -
''Leontodon hispidum L. Rough Hawkbit by 4 a.m. -
Helminthotheca echioides (L.) Holub Bristly ox-tongue 4-5 a.m.
Cichorium intybus L. Chicory 4-5 a.m. -
Crepis tectorum L. Hawk's Beard 4-5 a.m. -
Reichardia tingitana (L.) Roth - by 6 a.m. 10 a.m.
Sonchus oleraceus L. Sow thistle 5 a.m. 12 p.m.
Taraxacum officinale Weber Dandelion 5 a.m. 8-9 a.m.
Crepis alpina L. Hawk's beard 5 a.m. 11 a.m.
Tragopogon hybridus L. Goat's beard 5 a.m. 11 a.m.
Rhagadiolus edulis Gaertner - 5 a.m. 10 a.m.
Lapsana chondrilloides L. - 5 a.m. -
Convolvulus tricolor L. Bindweed, Morning Glory 5 a.m. -
Hypochaeris maculata L. Spotted cat's ear 6 a.m. 4-5 p.m.
Hieracium umbellatum L. Hawkweed 6 a.m. 5 p.m.
Hieracium murorum L. Hawkweed 6 a.m. 2 p.m.
Crepis rubra L. - 6 a.m. 1-2 p.m.
Sonchus arvensis L. Field milk-thistle 6 a.m. -
Sonchus palustris L. Marsh Sow-Thistle by 7 a.m. 2 p.m.
Leontodon autumnale L. Hawkweed 7 a.m. 3 p.m.
Hieracium sabaudum L. Hawkweed 7 a.m. 1-2 p.m.
Cicerbita alpina (L.) Wallr. Blue sow-thistle 7 a.m. 12 p.m.
Lactuca sativa L. Garden Lettuce 7 a.m. 10 a.m
Calendula pluvialis L. - 7 a.m. 3-4 p.m.
Nymphaea alba L. White Waterlily 7 a.m. 5 p.m.
Anthericum ramosum L. St. Bernard's Lily 7 a.m. -
Hypochaeris achyrophorus L. - 7-8 a.m. 2 p.m.
Hedypnois rhagadioloides (L.) Schmidt
subsp. cretica (L.) Hayck
- 7-8 a.m. 2 p.m.
Trichodiadema babrata (L.) Schwartes - 7-8 a.m. 2 p.m.
Hieracium pilosella L. Mouse-ear Hawkweed 8 a.m. -
Anagallis arvensis L. Scarlet pimpernell 8 a.m. -
Petrorhagia prolifera (L.) Ball & Heywood Proliferous Pink 8 a.m. 1 p.m.
Hypochaeris glabra L. Smooth cat's-ear 9 a.m. 1 p.m.
Malva caroliniana L. - 9-10 a.m. 1 p.m.
Spergularia rubra (L.) J. & C. Presl Sand spurrey 9-10 a.m. 2-3 p.m.
Mesembryanthemum crystallinum Ice-Plant 9-10 a.m. 3-4 p.m.
Cryophytum nodiflorum (L.) L. Bol. Ice-Plant 10-11 a.m 3 p.m.
Calendula officinalis L. Pot marigold - 3 p.m.
Hieracium aurantiacum Hawkweed - 3-4 p.m.
Anthericium ramosum L. (syn. Anthericum album) - - 3-4 p.m.
Alyssum alyssoides L. - - 4 p.m.
Papaver nudicaule L. Iceland poppy - 7 p.m.
Hemerocallis lilioasphodelus L. Day-lily - 7-8 p.m.

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