These popped up in our flower bed, close to where we planted some unknown pink flowered plants last year. They have tubular flowers, have maybe 10-12 stems per plant, each plant is slightly different in color, hot pink, lavender, deeper purple, pink.
this is called Cuphea, but I do not know the species. We have two native species of Cuphea, but this does not appear to be either of them. It looks like a nice cultivar that is persisting in your garden. I suggest that you look at images of Cuphea on Google and try to match one with this. I looked at some of them and could not find a perfect match.
Steve Hill, Botanist, SCNPS