Viola cucullata
Viola papilionacea
Common Blue Violet (Viola sororia). Ubiquitous in lawns, and there are some unaccountably dour types who try to eradicate it. Violets cause no harm; they never grow too high and are easily mowed, and they give us flowers like these. If you see a purple to pale blue violet in a neglected place, and especially if you see large numbers of them, this is probably the species.
Viola hirsutula
Viola fimbriatula
Viola sagittata
Viola triloba
Viola blanda
Viola pensylvanica
Viola canadensis
Viola striata
Johnny Jump-Up (Viola tricolor). This is the original Pansy, still so called in many places; it is every bit as colorful as our garden pansies, but smaller. It often escapes from plantings, and can occasionally establish itself in sidewalk cracks or vacant lots. Although it is associated with spring, it can bloom occasionally throughout the year