Some members of the willowherb family have large, bold, pink flowers whilst others are much more modest. Rosebay and great willowherb are in the former category whilst the less common marsh willowherb (Epilobium palustre) is undoubtedly in the second.
Marsh willowherb is one of several similar species with a few small, pale pink flowers appearing on stalks near the top of a single reddish coloured stem. It has opposite pairs of pointed, or lanceolate, leaves and this is helpful in identification because other similar species have alternate leaves that are often less narrow and pointed. The other distinguishing factor is that marsh willowherb grows in wet places on acid soils and that means it is the only willowherb likely to be found in ditches and marshy areas on the Dorset heaths.
Whilst not seemingly poisonous it seems that consuming this plant, especially the root, can have pretty nasty side effects including turning your face red and causing choking so it is best left alone!Marsh Willowherb:red faced