From the Proceedings of the Athanasius Kircher Society:
Linnaeus noted in his Philosophia Botanica that if one
possessed a sufficiently large variety of aequinoctal species, it would
be possible to tell time simply by observing the daily opening and
closing of flowers. Though Linneaus seems never actually to have
planted an horologium florae, or flower clock, his plan was
taken up with great passion by many 19th-century gardeners, who often
arranged a dozen or more species in the manner of a circular clock
face. Below, the approximate opening and closing times of aequinoctal flowers that can be used in an horologium florae:0200 – Night blooming cereus closes
0500 – Morning glories, wild roses
0600 – Spotted cat’s ear, catmint
0700 – African marigold, orange hawkweed, dandelions
0800 – Mouse-ear hawkweed, African daisies
0900 – Field marigold, gentians, prickly sowthistle closes
1000 – Helichrysum, Californium poppy, common nipplewort closes
1100 – Star of Bethlehem
1200 – Passion flower, goatsbeard, morning glory closes
1300 – Chiding pink closes
1400 – Scarlet pimpernel closes
1500 – Hawkbit closes
1600 – ‘Four o’clock’ plant opens, small bindweed closes, Californian poppy closes
1700 – White waterlily closes
1800 – Evening primrose, moonflower
1900
2000 – Daylilies and dandelions close
2100 – Flowering tobacco
2200 – Night blooming cereus