Selfheal

These appeared on a neighbours lawn, and worked out that they are selfheal.  Apparently it pops up in lawns that haven't been treated with chemicals, and the clusters of violet flowers appear from June to October, providing a nectar source for bees and wasps.

Also, as its common name suggests, selfheal has a long tradition of being used in herbal medicine for everything from stopping bleeding and healing wounds to treating heart disease and sore throats!