Gundermann is a species of flowering plant in the mint family. It can quickly spread throughout the lawn as well as in beds.
To eradicate Gundermann, you can also place one or more large pieces of cardboard, a heavy cloth or a black plastic tarpaulin over the plant. This prevents sunlight from reaching the plant, which is what it needs in order to grow. Since the herb has been used for centuries as a spice and medicinal plant, you could make a tea from the leaves.