Not 100% sure, but I’ve looked on several sources, including actual books, and it looks as though this is a Common Sorrel, which is in the same family as docks and knotweeds. Common sorrel grows on riverbanks as well as verges, grassland, and mountain ledges, so it’s not out of place in our watermeadow. It’s the sort of plant that I would usually overlook, but up close it is stunning with a multitude of tiny pink blossoms.