Here's something that popped up in a flower bed recently. At first I thought it was betony (noxious weed around here) but the leaves are quite different. It's also different from the perennial salvias I grow. The stem is square and there were tiny flowers (.5 mm or less) just below the very top set of leaves. The flowers have dropped off but they were a pink-lavender shade and the shape was like that of a foxglove or snapdragon flower (sorry, I don't know the terminology.) Any ideas?
Louisa, it's pretty close! The flowers on mine are smaller and paler in color. Funny you should mention lamium, though. I just bought a varegated one the other day and it looks suspiciously like my mystery weed!