Another one that was difficult to identify. Was it Greater or Lesser Stitchwort? The main difference is in the size of the flowers 0.5-1cm diameter for Lesser Stitchwort and 2-3cm for Greater Stitchwort. Also although they both have five distinctive split white petals, the Greater Stitchwort’s seem from photos to be broader in proportion to the length, making them seem more crowded, also they are slightly flared.
The Lesser Stitchwort flowers May-September. The name ‘Stellaria Graminea’ means star-like, grass-like, and indeed in USA, where it is an introduced species, it is known as the Grass-leaved Stitchwort. The name ‘Stitchwort’ refers to the plant’s use as a herbal cure for a stitch in the side.