Another plant popping up in the middle of things, for no apparent reason.
UPDATE: a couple more pictures for identification purposes.
UPDATE NUMBER 2: I figured out what it is. I was thinking, “It’s such an intense colour, the only time I’ve seen that shade of blue-purple— Oh.” So I looked it up. It’s an escapee from one of last year’s hanging baskets, or at least a seed must have escaped. I didn’t recognize it because I haven’t seen it as one tiny, spindly stalk before, just en masse.