Violaceae, the Violet Family
Herbs with simple, alternate or basal leaves, and conspicuous irregular flowers with a spur (except in the first species); sepals, petals, and stamens each 5; ovary 1-celled.
| 1a. Flowers regular or nearly so, greenish-white, axillary; erect plant with leafy stem (3-5 dm. high; spring) | Green Violet, Hybanthus concolor. |
| 1b. Flowers irregular, blue, yellow, or white, conspicuous (Violet) — 2. | |
| 2a. Plant stemless, the flowers all on leafless stalks and the leaves all basal (spring or early summer) — 3. | |
| 2b. Stems leafy (spring and summer) — 17. | |
| 3a. Petals yellow | Round-leaved Violet, Viola rotundifolia. |
| 3b. Petals blue, violet, or white — 4. | |
| 4a. Principal leaves at time of flowering deeply lobed — 5. | |
| 4b. Leaves oblong, ovate, or triangular, not narrowed to the petiole, and frequently sharply toothed or incised near the base — 7. | |
| 4c. Leaves narrowly lanceolate, tapering to the base | Violet, Viola lanceolata. |
| 4d. Leaves heart-shape or kidney-shape, not lobed — 8. | |
| 5a. Lateral petals bearded — 6. | |
| 5b. Lateral petals not bearded | Bird-foot Violet, Viola pedata. |
| 6a. Leaves divided to the base into linear segments | Bird-foot Violet, Viola pedatifida. |
| 6b. Leaves irregularly divided into broader segments | Hand-leaf Violet, Viola palmata. |
| 7a. Leaves ovate-oblong, pubescent | Violet, Viola fimbriatula. |
| 7b. Leaves triangular-lanceolate, usually somewhat dilated at base, nearly or quite glabrous | Violet, Viola sagittata. |
| 8a. Flowers violet or blue (rarely white-flowered plants are found with the typical blue-flowered ones) (Blue Violets) — 9. | |
| 8b. Flowers white, the 3 lower petals marked with purple (White Violets) — 14. | |
| 9a. Lateral petals bearded — 10. | |
| 9b. Lateral petals beardless | Great-spurred Violet, Viola selkirkii. |
| 10a. Foliage glabrous — 11. | |
| 10b. Petioles and lower surface of leaves pubescent — 13. | |
| 11a. Beard of the lateral petals with a knob at the tip of each hair | Blue Violet, Viola cucullata. |
| 11b. Beard of the lateral petals not knobbed — 12. | |
| 12a. Spurred petal hairy | Wood Violet, Viola affinis. |
| 12b. Spurred petal glabrous | Blue Violet, Viola papilionacea. |
| 13a. Spurred petal villous | Blue Violet, Viola septentrionalis. |
| 13b. Spurred petal glabrous, or with a few scattered hairs | Common Blue Violet, Viola sororia. |
| 14a. Leaf-blade obviously pubescent — 15. | |
| 14b. Leaf-blade glabrous or very nearly so — 16. | |
| 15a. Lateral petals bearded | Sweet White Violet, Viola incognita. |
| 15b. Lateral petals not bearded | White Violet, Viola renifolia. |
| 16a. Leaf-blades strictly glabrous | Sweet White Violet; Viola pallens. |
| 16b. Leaf-blades with some minute white hairs on the upper surface near the base | Sweet White Violet, Viola blanda. |
| 17a. Stipules large and leaf-like, deeply pinnatifid and nearly or quite as long as the petioles — 18. | |
| 17b. Stipules small, inconspicuous, entire or toothed, and much shorter than the petiole — 19. | |
| 18a. Leaves serrate; flowers 1.5-2.5 cm. wide (1-3 dm. high; flowers of various colors) | Pansy, Viola tricolor. |
| 18b. Upper leaves entire or nearly so; flowers about 1 cm. wide (1-2 dm. high; flowers bluish-white) | Wild Pansy, Viola rafinesquii. |
| 19a. Petals yellow (1-4 dm. high) (Yellow Violet) — 20. | |
| 19b. Petals violet, blue, or white — 21. | |
| 20a. Foliage villous-pubescent | Yellow Violet, Viola pubescens. |
| 20b. Foliage nearly or quite glabrous | Yellow Violet, Viola scabriuscula. |
| 21a. Stipules entire (2-4 dm. high) | Canada Violet, Viola canadensis. |
| 21b. Stipules toothed — 22. | |
| 22a. Lateral petals not bearded (1-2 dm. high) | Long-spurred Violet, Viola rostrata. |
| 22b. Lateral petals bearded — 23. | |
| 23a. Flowers white or nearly white (1-3 dm. high) | Pale Violet, Viola striata. |
| 23b. Flowers blue (about 1 dm. high) — 24. | |
| 24a. Leaves smooth | Dog Violet, Viola conspersa. |
| 24b. Leaves pubescent | Sand Violet, Viola arenaria. |