A violet seed pod. Don’t panic. It’s not going to get any bigger. But it will shoot seeds all over.

99% chance it’s a violet. 1% chance it’s a baby sandworm from planet Arrakis.

Wow, my wild violets never get those. I'm in zone 5b, Michigan, USA.

Are you sure? They’re very small. about 1/4 inch long. And if your Violets spread it’s pretty certain they set seed.

I've seen my violets for years and I've never seen anything but flowers and leaves. They are prolific but have a neat growth habit except in the late summer/fall when they get leggy. I will look at them carefully after the flowers bloom next spring to see if there are seeds. I hope so that would be fascinating.. I always supposed they spread by rhizomes.

I just nipped out the back door for two minutes to check and found this. It’s lost two of the three sections but it’s the same thing. These are our wild dog violets, Viola riviniana

I think this is the species I have. This reference says they spread by rhizome and seed. I've never seen my plants look like the picture with the seedpods. Next year I will be out there checking but I just think it's so strange I would not have noticed by now.

Violet (viola-papilionacea) pictures from UMass Amherst