There is a plant called Carpenter's Square. It's Latin name is Scrophularia marilandica. Another name for the plant is Maryland Figwort. In the photo below I have tried to darken the background for the whole plant so one can see the overall shape of the plant. This particular one was about 2 metres (6 feet) tall. I also included a side view and bottom view of the strange little flower on this plant as well as a close up look at the grooved square stem.
I have no idea why this plant is named "Carpenters Square," but shall try to find out. If someone knows, please drop a line and it will save some research time for me.