Blue Anise Sage, Brazilian Sage 'Black and Blue' (Salvia guaranitica)
I think this is what I have in my garden that is absolutely taking over. Could it be. I have no pictures at this time. I have been trying half-heartedly to find out what it is for about 3 years now. It is very pretty but the more I pull the more it spreads. Someone, who didn't know what it was either, told me it spread by self-seeding, but I think it sends out runners.