There were several to be found here. This second one was also at the Observatory high on the wall. There was no sun to throw shadows on either of these.
A clock on the wall at Winterbourne Botanical Gardens at Birmingham University depicts a floral clock. This idea was originally created by Carl Linnaeus in 1751. It shows the plan for a floral clock garden with flowers planted according to the time of day the flowers are likely to be open and thus tell the time by them.
Then finally. How else can you tell the time? The old faithful of the Dandelion Clock. How many of these have you blown in your childhood?