This is commonly called the Shamrock Plant or otherwise is known as the Wood Sorrel (Oxalis acetosella).
It likes moist well-drained soil, shady areas and self seeds itself freely… so Botanica says. The leaves fold themselves at night.
Doesn’t the shape of the leaves look like the wings of a moth and doesn’t the photo look like a posse of moths have come to rest in a mound on the plant?
NATURE IN JAPAN 