2016-05-15-10-46 Marsh marigold

Ranunculus rembrantes

cosme.fi - Flowers in Finland

Fun traditions!
This is a familiar April Fool's joke! It often continues:
April Fools, eat herring, drink muddy water on top — and nothing on top!

Or in some versions:
April, eat herring, drink muddy water on top — and no shame at all!