Viola sororia, common blue violet
This lovely plant is one of our most common native species. It makes a beautiful groundcover, especially in spring. The leaves of this plant are favored as food by caterpillars of fritillary butterflies. Even if you spend a lot of time watching violets you might not see the caterpillar because it is very secretive. It will leave the plant and hide out in dead leaves nearby, perhaps only feeding at night. The Regal Fritillary is one of the rarest butterflies in the state, so you likely won't see that one. But if we're lucky, maybe our violets will rear a Great Spangled Fritillary, like the one on the left. You won't see the adult butterfly on the violets, because they don't make nectar. But in the late summer check out milkweeds and joepye weeds for these lovely butterflies.
So why do some people think violets are weeds? Well, it is true that violets spread a lot, but that's a good feature in a ground cover! When selective herbicides like 2,4-D became widely available, everything but grass in the lawn because a weed, because this herbicide kills everything but grass in the lawn. Nowadays people concerned about the plants and animals we share the planet with may prefer to consider plants like blue violets, which are after all native plants, to be desirable lawn residents.