It looks like some type of Triodanis Perfoliata. Maybe 'Clasping Venus'. I have these in purple, but I live in NY.

Looks a little like a campanula variety?

I'd go for one of the carpeting campanula too. there are several species that have this habit. easy to pull out, but they seed prolifically.

Campanula portenschlagiana aka C. muralis. A real thug of a campanula it is too.

Best kept in check - it has a mind of its own.

Triodanis Perfoliata IS in the campanula family. Same for Venus' Looking Glass. However, this one is very weedy and hard to keep in check.

Triodanis perfoliata. Triodanis perfoliata, the clasping Venus' looking-glass or clasping bellflower, is a flowering plant belonging to the family Campanulaceae. It is an annual herb native to North and South America, the natural range extending from Canada to Argentina.

I have/had campanula, however, it seems to get eaten by some “bug” on my rockery! Maybe a good thing?

Thanks for all your comments. I looked up images on the net and think mine might be Campanula Poscharskyana.

I do like that periwinkle blue. Not a common color in nature.