Flower:

Single irregular 5-petaled flower at the end of a long, naked stalk arising from a leaf axil. Flowers are pale blue to violet with a white throat, up to ~2/3 inch (≤ 17 mm) long. The upper two petals are erect or bent back, the two lateral petals have fine hairs at the base (bearded), the lower petal is hairless, has purple veins near the base, and forms a long rounded spur at the back.

The 5 sepals around the base of the flower are hairless, the two lower largest, narrowly lance-shaped to linear, tapering to a pointed tip, and have a short or distinct extension at the base (auricle) that may be irregularly shaped along the end and does not elongate much in fruit.

Leaves and stem:

There are both basal leaves and stem leaves; color is light to medium yellow-green. Both are up to about 1¼ inches (to 31 mm) long and about as wide, round to kidney to heart-shaped with a blunt or rounded tip. Edges are scalloped, surfaces are mostly hairless, sometimes with sparse appressed hairs on the upper surface. At the base of a leaf stalk is a pair of leafy appendages (stipules), lance-elliptic with a few teeth along the edge. Stems are hairless, with multiple leafy stems arising from the base. Loose colonies may form from long rhizomes.

Fruit:

Both petalled (chasmogamous) and petal-less, self-pollinating (cleistogamous) flowers produce fruit, in an ovoid capsule that becomes erect just before splitting into 3 sections and releasing its seed. Chasmogamous flowers bloom in spring. Cleistogamous flowers are produced all summer. All capsules are about ¼ inch (3 to 6 mm) long, green drying tan, with or without fine red spots.

Seeds are light to medium brown, 1.5 to 2 mm long.

Notes:

There are numerous species of blue or purple violets that grow in Minnesota. Three distinguishing features in identifying them are whether the flowers and leaves come from the same stem, whether petals are bearded, and whether leaves, stems and stalks are hairy. The first two are true for Dog Violet, formerly known as Viola conspersa; it is further distinguished by essentially hairless, yellow-green leaves mostly rounded at the tip and heart-shaped at the base, and its flowers are notably paler blue to violet. It is often confused with Sand Violet (Viola adunca), which also has both stem and basal leaves, but flowers are darker purple, is usually noticeably hairy on leaves, stems and stalks, leaves are more blue-green in color, more triangular to egg-shaped, blunt to rounded at the tip, and rounded to straight across to barely heart-shaped at the base. These two species have been known to hybridize but there are no records of this hybrid in Minnesota.

Of note is some references mention differences in the stipules between V. adunca and V. labradorica, specifically the former being more strongly incised/toothy than the latter, but I have seen a lot of variation in both species so found that to be unreliable in the field.