First pic is Broad-leaved Willowherb (Epilobium montanum), showing its relatively (for a willowherb) broad leaves and its four-lobed stigma. Pics two and three show Square-stalked Willowherb (Epilobium tetragonum) with its club-shaped stigma, its narrower leaves and its square stalk. The light and shadow on the stem in pic three does show two distinct sides of the stalk though it’s easier to detect this characteristic if one rolls the stalk between one’s fingers. The supposed conspicuousness of the stem corner ridges is not very apparent on this specimen.