I couldn't find a taxonomic key listing all of Saskatchewan Violet species, so after researching most of the species, I've put this key together for my own use. An important part of this key is flower colour, which is most important to me as a plant photographer - I'm interested in identifying and photographing the plants when in bloom. Note the very rare V. labradorica is not included; nor the introduced Johnny Jump-Up/Pansy species: V. bicolor, V. tricolor, V. arvensis.

Some of this key is taken from an article Violets of Saskatchewan, by Dr. Vernon Harms, Blue Jay magazine, June 1973.

1 a) Flowers yellow go to 2
1 b) Flowers purple-blue or mauve go to 3
1 c) Flowers white go to 8

2 a) Plants 20 to 40 cm tall, leaves ovate with cordate bases, flowering stems leafy at the top, stems covered in downy hairs - the plant is Viola pubescens.
2 b) Plants less than 20 cm tall, leaves mostly basal, leaves lanceolate and tapering at the base, leaves usually at least 3 times as long as wide - the plant is Viola nuttallii.
2 c) Plants less than 20 cm tall, leaves mostly basal, leaves ovate with cordate or truncate bases, the leaves less than 3 times as long as wide - the plant is Viola vallicola.

3 a) Leaves cleft almost to their bases - the plant is Viola petafida.
3 b) Leaves not deeply divided or lobed, merely shallowly toothed go to 4.

4 a) Plant has leafy flowering stems - the plant is Viola adunca.
4 b) Plant without a leafy flowering stem, the leaves and flower stem all grow from a central rootstalk go to 5.

5 a) Petals beardless, flower spur is long, about 2/3 the length of the petal blade - the plant is Viola selkirkii.
5 b) Side petals or all petals bearded go to 6

6 a) Some leaf stems with hairy petioles - the plant is Viola sororia.
6 b) Plants glabrous go to 7

7 a) Plants have a thick rootstalk and no runners, flowers blue-purple - the plant is Viola nephrophylla.
7 b) Plants have a slender rootstalk with runners, flowers pale mauve - the plant is Viola palustris.

8 a) Flowering stems with leaves, plants large 20 to 60 cm in height - the plant is Viola canadensis var. rugulosa.
8 b) Flowering stems without leaves go to 9.

9 a) Lateral petals bearded go to 10
9 b) Lateral petals beardless or with an inconspicuous tuft of hairs, leaves less than or equal to 2.5 cm wide and long, scapes noticeably elongate, wetland habitat, underside of leaves hairless - the plant is Viola macloskeyi.
9 c) Lateral petals beardless, undersides of leaves with a few hairs, leaves wider than long - the plant is Viola renifolia.

10 a) Petioles sparsely hairy to puberulent, leaf undersides with hairs, some leaves greater than or equal to 2.5 cm wide and long - the plant is Viola blanda.
10 b) Plants glabrous, found in Porcupine Hills, plants have a slender rootstalk with runners  - the plant is Viola palustris.