Flower:

Single irregular 5-petaled flower at the end of a minutely hairy stalk arising from a leaf axil. Flowers are purple to blue-violet with a white throat, up to ~2/3 inch (≤ 16 mm) long. The upper two petals are erect or bent back, the two lateral petals have short hairs at the base (bearded), the lower petal is hairless, has purple veins near the base, and forms a short rounded spur at the back.

The 5 sepals around the base of the flower are hairless or minutely hairy along the midvein, the two lower largest, narrowly lance-shaped to linear, tapering to a pointed tip, and have a short or prominent extension at the base (auricle) that may be notched along the end and may elongate some in fruit.

Leaves and stems:

There are both stem and basal leaves; color is blue-green. Leaves are up to 1½ inches (to 4 cm) long, ½ to 1 inch wide, triangular to egg-shaped, rounded to straight across to slightly heart-shaped at the base, rounded or blunt at the tip, and on a long stalk. Leaf edges are scalloped to nearly toothless and often fringed with minute hairs; surfaces are minutely hairy, especially the lower surface.

At the base of a leaf stalk is a pair of leafy appendages (stipules) that are typically narrow with a few long, slender teeth or lobes. Stems are usually minutely hairy, rarely hairless, with multiple leafy stems arising from the base.

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 1/3 inch (6 to 9 mm) long, green drying tan, with or without fine red spots.

Seeds are medium to dark 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. All three are true for Sand Violet; it is further distinguished by its blue-green leaves that are rounded to straight across to somewhat heart-shaped at the base, and long spur on the flowers. It is often confused with Dog Violet (Viola labradorica a.k.a. V. conspersa), which also has both stem and basal leaves, but it is hairless, flowers are a paler violet, leaves are more yellow-green in color and more strongly 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.