Hey Bjorn. The plant you show is called Motherwort, Leonurus cardiaca. It does grow in clumps. Very attractive to bees. In the mint family...square stem. Related to Catnip. Plant was formerly used in medicine, especially for diseases of women...whatever that means. American Honey Plants, Frank C Pellett
Yes It is Motherswort. Still used in folk medicine by some folks and at one time a major plant for use by women.
If you want to know the women use just goggle the plant.
I have a friend who harvest the seeds and spread them all over the place because bees do love them.
I know I'm adding this to the plants I'll be expanding at the farm. The bees love this plant. One site called it a perennial, so I going to mark the plants and if they sprout again in the spring, I'll be making some beds.
Seeds do seem to be available at several suppliers. This would be a great background plant for flower beds as it lasts all summer and flowers for a long time, growing several feet high.