Small herbs or shrubs, with opposite or alternate entire leaves; flowers regular, with 5 sepals, 3 or 5 petals, and 3 to many stamens.
| 1a. Flowers yellow (early summer) [— 2.] | |
| 1b. Flowers greenish or purplish, minute, in panicles (late summer) (Pinweed) [— 4.] | |
| 2a. Leaves crowded, closely appressed to the branches; flowers 7 mm. wide (2-4 dm. high) | False Heather, Hudsonia tomentosa. |
| 2b. Leaves spreading; flowers 15-30 mm. wide (3-6 dm. high) (Frostweed) [— 3.] | |
| 3a. Petal-bearing flowers solitary | Frostweed, Helianthemum canadense. |
| 3b. Petal-bearing flowers few, racemose | Frostweed, Helianthemum majus. |
| 4a. Stem-leaves linear, 4 or more times as long as wide [— 5.] | |
| 4b. Stem-leaves oblong or elliptical, about 3 times as long as wide (2-6 dm. tall) [— 8.] | |
| 5a. Plant pale with dense appressed pubescence (2-4 dm. high) | Pinweed, Lechea stricta. |
| 5b. Plant green, pubescence sparse or none [— 6.] | |
| 6a. Leaves thread-like, seldom exceeding 1 mm. in width (1-3 dm. tall) | Pinweed, Lechea tenuifolia. |
| 6b. Leaves 1-5 mm. wide (2-6 dm. high) [— 7.] | |
| 7a. Leaves on the basal shoots narrowly lanceolate | Pinweed, Lechea intermedia. |
| 7b. Leaves on the basal shoots oblong-elliptic, about twice as long as wide | Pinweed, Lechea racemulosa. |
| 8a. Pubescence of spreading hairs | Pinweed, Lechea villosa. |
| 8b. Pubescence of appressed hairs | Pinweed, Lechea minor. |
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. |
CACTACEAE, the Cactus Family
Fleshy, jointed leafless plants, armed with numerous thorns; flowers large (5-10 cm. wide), yellow, with about 10 petals and numerous stamens.
| One species in Michigan, on the shores of Lake Michigan; flowers in summer | Prickly Pear, Opuntia rafinesquii. |