Common Wood Sorrel Oxalis acetosella
Common wood sorrel is a plant from the genus Oxalis, common in most of Europe and parts of Asia. It flowers for a few months during the spring, with small white flowers with pink streaks. Red or violet flowers also occur rarely. The binomial name is Oxalis acetosella, because of its sour taste.
The leaflets are made up by three heart-shaped leaves, folded through the middle. The stalk is red/brown, and during the night or when it rains both flowers and leaves contract.
Historically, people have extracted calcium oxalate, or "sal acetosella" from the plant, through boiling. It is slightly toxic, as oxalic acid is known to interfere with food digestion.
The common wood sorrel is sometimes referred to as a shamrock (due to its three-leaf clover-like motif) and given as as gift on St. Patrick's Day.
from wikipedia ( dutch name: witte klaverzuring)