Lonely petunia in an onion patch

Well not quite, but close enough. These flowers are like weeds and come up all over the show. They do not have seeds so I am not sure how they propagate themselves, but I do know the ants love them. They have pink and white flowers and grow to a height of about 3 foot. Very often they are found in places like this:
There is not a scrap of soil in this rock so it is putting out roots on the side.