I think Violets will grow anywhere almost. Johnny JumpUps, aren't they a type of violet? Jane, your violets are probably happily marching across your lawn as they reseed themselves annually. Can you tell where they originally started in at? Would be interesting to detect their line of advancement. Would probably let you know which areas of your yard has the more desirable elements for them.
I was weeding a couple of raised beds yesterday when I remembered one of them is 'invaded' with Johnnys every Spring. I can't remember what the leaf structure is like, strap, serrated? I don't think they've popped out of the ground yet, but I wouldn't want to yank them along with the henbit. Speaking of ... (henbit) is that stuff good for anything? I appreciate it because it gives up and pulls out so easily. (I almost can't call it a weed because of that.)