Herbs with alternate (rarely opposite) leaves, acrid watery juice, separate sepals and petals, numerous stamens, and several or many (rarely only 1) simple pistils. Petals present or absent, in the latter case the sepals are usually petal-like in appearance.
| 1a. Climbing plants with opposite leaves (flowers in late summer) (Virgin's Bower) — 2. | |
| 1b. Aquatic plants with dissected submerged leaves (flowers in late spring and summer) (Water Crowfoot) — 3. | |
| 1c. Terrestrial or mud plants, not agreeing with 1a or 1b — 6. | |
| 2a. Flowers white, 2-3 cm. wide | Virgin's Bower, Clematis virginiana. |
| 2b. Flowers pink-purple, 5-8 cm. wide | Virgin's Bower, Clematis verticillaris. |
| 3a. Flowers white — 4. | |
| 3b. Flowers yellow — 5. | |
| 4a. Leaves rigid, not collapsing when removed from the water | Water Crowfoot, Ranunculus circinatus. |
| 4b. Leaves soft, collapsing when removed from the water | Water Crowfoot, Ranunculus aquatilis var. capillaceus. |
| 5a. Submerged leaves divided into hair-like segments | Water Crowfoot, Ranunculus delphinifolius. |
| 5b. Submerged leaves palmately divided into linear lobes | Water Crowfoot, Ranunculus purshii. |
| 6a. Flowers blue, irregular, with one spur (4-8 dm. high, summer) | Larkspur, Delphinium ajacis. |
| 6b. The five petals each prolonged into a spur; flowers showy (4-8 dm. tall) (Columbine) — 7. | |
| 6c. Flowers regular, without spurs — 8. | |
| 7a. Spurs nearly straight; flowers scarlet and yellow (spring) | Wild Columbine, Aquilegia canadensis. |
| 7b. Spurs strongly incurved; flowers blue or white (spring, early summer) | Columbine, Aquilegia vulgaris. |
| 8a. Flowers yellow — 9. | |
| 8b. Flowers of various colors, but never yellow — 28. | |
| 9a. Petals none; sepals petal-like; leaves crenate or dentate (2-4 dm. high, flowers in early spring) | Cowslip, Caltha palustris. |
| 9b. Petals small; sepals petal-like; leaves deeply palmately lobed (4-6 dm. tall; flowers in late spring) | Globe-flower, Trollius laxus. |
| 9c. Petals yellow; sepals green or yellowish — 10. | |
| 10a. Leaves linear to narrowly oblong, entire or with minute teeth (flowers 10-15 mm. wide, in summer) — 11. | |
| 10b. Leaves broader, some or all of them lobed or divided, or cordate-ovate and not lobed — 12. | |
| 11a. Stems ascending (4-8 dm. high), rooting at the lower joints; fruits pointed with a long slender beak | Spearwort, Ranunculus laxicaulis. |
| 11b. Stems prostrate and trailing, rooting at the joints; fruits tipped with a minute short beak | Spearwort, Ranunculus flammula var. reptans. |
| 12a. Basal leaves, or most of them, merely serrate or crenate, and not obviously lobed — 13. | |
| 12b. All the leaves lobed or divided — 16. | |
| 13a. Stem-leaves resembling the basal ones, and not lobed (1-2 dm. high; summer) | Sea-side Crowfoot, Ranunculus cymbalaria. |
| 13b. Stem-leaves deeply divided into oblong or linear segments — 14. | |
| 14a. Flowers 1.5 cm. wide or more (1-3 dm. high; spring) | Buttercup, Ranunculus rhomboideus. |
| 14b. Flowers 1 cm. wide or less (2-5 dm. high; spring) — 15. | |
| 15a. Foliage glabrous or minutely pubescent; basal leaves cordate | Small-flowered Crowfoot, Ranunculus abortivus. |
| 15b. Foliage villous; basal leaves barely cordate or not at all | Small-flowered Crowfoot, Ranunculus micranthus. |
| 16a. Stem erect or essentially so — 17. | |
| 16b. Stem prostrate, creeping, or ascending. Early in spring stems may be found which appear almost erect. Common spring-flowering buttercups are all classified here — 22. | |
| 17a. Flowers 2 cm. broad or larger (Buttercup) — 18. | |
| 17b. Flowers 1 cm. broad or smaller — 19. | |
| 18a. Terminal lobe of leaf stalked (2-5 dm. high, early summer) | Buttercup, Ranunculus bulbosus. |
| 18b. Terminal lobe of leaf sessile (5-10 dm. high; all summer) | Buttercup, Ranunculus acris. |
| 19a. Plant glabrous, succulent; stem hollow (1-5 dm. high; spring and summer) | Cursed Crowfoot, Ranunculus sceleratus. |
| 19b. Plant pubescent (Buttercup) — 20. | |
| 20a. Fruits tipped with a prominent recurved beak; plant of shady woods (2-6 dm. high; flowers in late spring) | Buttercup, Ranunculus recurvatus. |
| 20b. Fruits tipped with a straight or slightly curved beak; plants of marshes or wet soil (3-6 dm. high; flowers in summer) — 21. | |
| 21a. Fruits in a short-cylindric head on a conical receptacle | Buttercup, Ranunculus pennsylvanicus. |
| 21b. Fruits in a globose or short-ovoid head, on an obovoid receptacle | Buttercup, Ranunculus macounii. |
| 22a. Leaves dissected into numerous linear or narrowly wedge-shape divisions; plants growing in water or very wet places (late spring and summer) | Water Crowfoot, Ranunculus delphinifolius. |
| 22b. Leaves palmately lobed, the terminal division not definitely stalked — 23. | |
| 22c. Leaves compound, some or all of the divisions on definite stalks (Buttercup) — 24. | |
| 23a. Stem-leaves numerous (1-2 dm. tall; late spring and summer) | Crowfoot, Ranunculus purshii. |
| 23b. Stem-leaves one or none, the principal leaves all basal (about 1 dm. high; flowers in summer) | Buttercup, Ranunculus lapponicus. |
| 24a. Style short, obviously curved — 25. | |
| 24b. Style long and slender, straight or nearly so (common spring-flowering buttercups, 2-5 dm. high) — 26. | |
| 25a. Stems creeping; flowers 2 cm. wide or more (spring) | Buttercup, Ranunculus repens. |
| 25b. Stems ascending; flowers 1.5 cm. wide or less (3-6 dm. high; summer) | Buttercup, Ranunculus macounii. |
| 26a. The two lateral divisions of the leaf sessile or nearly so | Buttercup, Ranunculus fascicularis. |
| 26b. The two lateral divisions of the leaf on long stalks — 27. | |
| 27a. Roots fibrous; plants of wet soil | Buttercup, Ranunculus septentrionalis. |
| 27b. Roots thickened; plants of dry woods or thickets | Buttercup, Ranunculus hispidus. |
| 28a. Leaves dissected into numerous narrowly linear acute divisions (4-7 dm. high; flowers large, bluish, in summer) | Love-in-a-mist, Nigella damascena. |
| 28b. Leaves lobed or divided, but the divisions not separated by definite stalks — 29. | |
| 28c. Leaves truly compound, all their divisions separated by distinct stalks — 39. | |
| 29a. Leaves all basal, their lobes (usually 3) entire (1-2 dm. high; flowers pink-purple, in earliest spring) (Hepatica) — 30. | |
| 29b. Lobes of the leaf serrate or incised — 31. | |
| 30a. Lobes of the leaf obtuse or rounded | Hepatica, Hepatica triloba. |
| 30b. Lobes of the leaf acute | Hepatica, Hepatica acutiloba. |
| 31a. Petals none; sepals 3, usually falling away as soon as the flower opens (2-4 dm. high; flowers greenish-white, in spring) | Golden Seal, Hydrastis canadensis. |
| 31b. Petals none; sepals petal-like, 4 or more (Anemone) — 32. | |
| 31c. Petals present, but much smaller than the 5 petal-like sepals — 38. | |
| 32a. Stem-leaves sessile or nearly so — 33. | |
| 32b. Stem-leaves on definite petioles — 35. | |
| 33a. Ovary tipped with a long slender hairy style; flowers bluish-purple (1-4 dm. high; early spring) | Pasque Flower, Anemone patens var. wolfgangiana. |
| 33b. Ovary with a short style, densely woolly; flowers red, greenish, or white (1-4 dm. high; late spring and summer) — 34. | |
| 33c. Ovary tipped with a short style, glabrous or nearly so; flowers white (4-7 dm. high; late spring and early summer) | Anemone, Anemone canadensis. |
| 34a. Stem 1-flowered, sepals white | Anemone, Anemone parviflora. |
| 34b. Stem 3-flowered; sepals usually red | Anemone, Anemone multifida. |
| 35a. Achenes densely woolly; flowers appearing in summer — 36. | |
| 35b. Achenes merely pubescent; stems 1-flowered; woodland species blooming in early spring (1-2 dm. high; flowers white) | Wood Anemone, Anemone quinquefolia. |
| 36a. Segments of the leaf broadly wedge-shape or ovate; flowers white (4-8 dm. high) — 37. | |
| 36b. Segments of the leaf linear-oblong; flower red, greenish, or white; plants growing on the shores of the Great Lakes | Anemone, Anemone multifida. |
| 37a. Segments of the basal leaves wedge-lanceolate; head of fruit cylindric | Anemone, Anemone cylindrica. |
| 37b. Segments of the basal leaves ovate-lanceolate; head of fruit ovoid or oblong | Anemone, Anemone virginiana. |
| 38a. Stem-leaves present — 9b. | |
| 38b. Leaves all basal (1-2 dm. high; leaves 3-divided; flowers white, in early summer) | Gold-thread, Coptis trifolia. |
| 39a. Flowers numerous, in branching panicles (Meadow Rue) — 40. | |
| 39b. Flowers numerous, in racemes — 43. | |
| 39c. Flowers solitary or few, in loose clusters; woodland plants blooming in early spring (1-3 dm. high; flowers white to purple) — 45. | |
| 40a. Blooming in spring; stem-leaves with obvious petioles (3-7 dm. high; flowers white or greenish) | Meadow Rue, Thalictrum dioicum. |
| 40b. Blooming in late spring or summer, stem-leaves sessile or nearly so (8-15 dm. high; flowers white) — 41. | |
| 41a. Filaments club-shape, approximately as wide as the anther | Meadow Rue, Thalictrum polygamum. |
| 41b. Filaments slender or thread-like — 42. | |
| 42a. Leaves minutely pubescent beneath, but not glandular | Meadow Rue, Thalictrum dasycarpum. |
| 42b. Leaves minutely glandular beneath | Meadow Rue, Thalictrum revolutum. |
| 43a. Racemes slender, 10-90 cm. long (8-15 dm. high; flowers white, in summer) | Bugbane, Cimicifuga racemosa. |
| 43b. Racemes short and stout, 3-8 cm. long (4-8 dm. high; flowers white, in late spring) (Baneberry) — 44. | |
| 44a. Berries white; pedicels strongly thickened at maturity | Baneberry, Actaea alba. |
| 44b. Berries red; pedicels slender | Baneberry, Actaea rubra. |
| 45a. Flowers white; stem-leaves alternate | Isopyrum, Isopyrum biternatum. |
| 45b. Flowers white to pink or purplish; stem-leaves whorled | Rue Anemone, Anemonella thalictroides. |
Trees or shrubs, with alternate leaves, and large, frequently showy flowers.
| One species in Michigan, with broad 4-lobed leaves and greenish-yellow flowers in late spring | Tulip Tree, Liriodendron tulipifera. |
Trees or shrubs, with alternate simple entire leaves, 3 sepals, and 6 petals.
| One species in Michigan; tall shrub or small tree, with obovate leaves and large dull-purple flowers in spring | Papaw, Asimina triloba. |
Woody climbers, with alternate leaves, 6-8 petals, and numerous stamens.
| One species in Michigan, with 5-7-angled leaves which are peltate near the edge, and small white flowers in early summer | Moonseed, Menispermum canadense. |
Shrubs or herbs; petals 6 or more; stamens 6-18, frequently opening by two terminal lids; pistil 1.
| 1a. Leaves simple — 2. | |
| 1b. Leaves compound — 3. | |
| 2a. Stem shrubby (flowers yellow, in racemes, in spring) | Barberry, Berberis vulgaris. |
| 2b. Stem herbaceous, with a single pair of palmately lobed leaves (4-6 dm. tall; flower white, solitary, terminal, in spring) | May Apple, Podophyllum peltatum. |
| 3a. Leaves all basal; leaflets 2 (2-4 dm. high; the flower-stalks bearing solitary white flowers in spring) | Twin-leaf, Jeffersonia diphylla. |
| 3b. The stem-leaf ternately compound, with numerous leaflets (4-8 dm. high; with yellowish-green clustered flowers in spring) | Blue Cohosh, Caulophyllum thalictroides. |
Trees or shrubs, with aromatic taste or odor, and alternate simple leaves; flowers small, imperfect, the anthers opening by lids.
Herbs with milky or colored juice, regular flowers, 2 sepals, 4, 6, or 8 petals, numerous stamens, and a 1-celled ovary.
| 1a. Leaves palmately lobed; flower 2.5-5 cm. wide, with 8 petals or more (leaf basal; flower white, in early spring) | Bloodroot, Sanguinaria canadensis. |
| 1b. Leaves pinnately toothed or lobed; flower 7-10 cm. wide, with 4-6 petals (4-8 cm. high; leaves clasping; summer) | Poppy, Papaver somniferum. |
| 1c. Leaves divided pinnately to the mid-rib into several toothed or lobed segments; flower 2.5 cm. broad or less (3-5 cm. high; flowers yellow) — 2. | |
| 2a. Flowers in clusters of 2-4, about 3 cm. wide (spring) | Celandine Poppy, Stylophorum diphyllum. |
| 2b. Flowers in umbels of 3-8, about 1.5 cm. wide | Celandine, Chelidonium majus. |
Herbs with watery juice, compound or dissected leaves, and irregular flowers; sepals 2, small; petals 4, in two pairs, and one or both of the outer pair spurred at the base; stamens 6.
| 1a. Both outer petals spurred or sack-like at the base — 2. | |
| 1b. One outer petal spurred or sack-like at the base — 4. | |
| 2a. A climbing vine with flowers in panicles (white or pinkish flowers in summer) | Climbing Fumitory, Adlumia fungosa. |
| 2b. Low herbs (2-4 cm.) with basal leaves and white or pinkish flowers in racemes (early spring) — 3. | |
| 3a. Spurs of the corolla triangular, divergent | Dutchman's Breeches, Dicentra cucullaria. |
| 3b. Spurs of the corolla short and rounded | Squirrel Corn, Dicentra canadensis. |
| 4a. Flowers about 5 mm. long, pink-purple tipped with red (3-8 dm. high; summer) | Fumitory, Fumaria officinalis. |
| 4b. Flowers 10 mm. long or more, yellow, at least at the tip (2-6 dm. high) (Corydalis) — 5. | |
| 5a. Flowers yellow throughout (spring) | Corydalis, Corydalis aurea. |
| 5b. Flowers pink, tipped with yellow (summer). | Corydalis, Corydalis sempervirens. |
Herbs, with alternate, frequently lobed or dissected leaves, and regular flowers, usually in racemes; sepals and petals each 4, stamens 6, 4 long and 2 short (or rarely 2 only), ovary 1.
| 1a. Petals yellow or yellowish — 2. | |
| 1b. Petals white, pink, or purple, never yellow — 29. | |
| 2a. Leaves simple, entire or dentate, never lobed — 3. | |
| 2b. Leaves deeply lobed or compound (the bracteal leaves, at or near the flower-clusters, may be simple and unlobed) — 10. | |
| 3a. Leaves clasping the stem — 4. | |
| 3b. Leaves not clasping at base — 6. | |
| 4a. Clasping base and apex of leaf obtuse or rounded; pod very long and slender (3-8 dm. high; summer) | Hare's Ear, Conringia orientalis. |
| 4b. Clasping base and apex of leaf acute; pod obovoid (3-7 dm. high; early summer) (False Flax) — 5. | |
| 5a. Stem and leaves glabrous | False Flax, Camelina sativa. |
| 5b. Leaves and usually the stem pubescent | False Flax, Camelina microcarpa. |
| 6a. Flowers about 2 mm. wide (1-3 dm. high; flowers in summer) — 7. | |
| 6b. Flowers 5 mm. wide or more (2-6 dm. high; flowers in summer) — 8. | |
| 7a. Leaves about twice as long as broad, widest near or below the middle | Whitlow Grass, Draba nemorosa. |
| 7b. Leaves 3-5 times as long as broad, widest above the middle | Yellow Alyssum, Alyssum alyssoides. |
| 8a. Leaves lanceolate, gradually tapering to the base; flowers about 15 mm. wide | Sand Rocket, Diplotaxis muralis. |
| 8b. Leaves ovate, acute at base; flowers about 15 mm. wide — 22a. | |
| 8c. Leaves entire or minutely toothed; flowers 5-10 mm. wide — 9. | |
| 9a. Pods 25 mm. long or less, on slender pedicels about 8 mm. long | Worm-seed Mustard, Erysimum cheiranthoides. |
| 9b. Pods 20 mm. long or more, on stout pedicels about 4 mm. long | Worm-seed Mustard, Erysimum parviflorum. |
| 10a. Leaves bipinnate or dissected into very numerous divisions (3-8 dm. high; flowers in summer) — 11. | |
| 10b. Leaves simply pinnate — 13. | |
| 11a. Flowers about 5 mm. broad; pods about 20 mm. long by 1 mm. broad | Herb Sophia, Sisymbrium sophia. |
| 11b. Flowers about 3 mm. broad; pods about 8 mm. long by 2 mm. wide (Tansy Mustard) — 12. | |
| 12a. Stems gray with a close fine pubescence | Tansy Mustard, Sisymbrium canescens. |
| 12b. Stems green | Tansy Mustard, Sisymbrium canescens var. brachycarpon. |
| 13a. Pod short, not more than 3 times as long as wide (coarse plants, preferring wet or sandy ground; flowers in summer) (Yellow Cress) — 14. | |
| 13b. Pod elongated, more than 4 times as long as wide — 17. | |
| 14a. Stems creeping, with erect or ascending branches; flowers about 8 mm. wide | Yellow Cress, Radicula sylvestris. |
| 14b. Stems erect or ascending (3-10 dm. high); flowers about 4 mm. wide — 15. | |
| 15a. Pods about twice as long as the pedicels | Yellow Cress, Radicula obtusa. |
| 15b. Pods about as long as the pedicels, or shorter than them — 16. | |
| 16a. Plant glabrous or minutely pubescent | Yellow Cress, Radicula palustris. |
| 16b. Plant hirsute | Yellow Cress, Radicula palustris var. hispida. |
| 17a. Petals 7 mm. long or more; pod terminating in a conspicuous beak (coarse, weedy plants, 3-12 dm. high, blooming in summer) — 18. | |
| 17b. Petals of smaller size; pod not terminating in a conspicuous beak — 24. | |
| 18a. Upper stem-leaves clasping at the base | Rutabaga, Brassica campestris. |
| 18b. Upper stem-leaves not clasping — 19. | |
| 19a. Pod tipped with a slender cylindrical beak whose base is much narrower than the pod — 20. | |
| 19b. Pod gradually narrowed at its tip into a stout, flattened or angled beak — 22. | |
| 20a. Leaves oblanceolate, rather regularly pinnatifid, the terminal segment about the same size as the lateral ones | Sand Rocket, Diplotaxis muralis. |
| 20b. Leaves broad, irregularly pinnatifid especially below the middle, with a large terminal segment — 21. | |
| 21a. Beak of pod 3-4 mm. long | Black Mustard, Brassica nigra. |
| 21b. Beak of pod 5 mm. long or more | Indian Mustard, Brassica juncea. |
| 22a. Leaves dentate or lobed | Charlock, Brassica arvensis. |
| 22b. Leaves deeply pinnatifid — 23. | |
| 23a. Pod dehiscent when ripe by two valves, tipped with a flat or angled beak | White Mustard, Brassica alba. |
| 23b. Pod indehiscent, with spongy cross-partitions between the seeds, tipped with a conical beak | Wild Radish, Raphanus raphanistrum. |
| 24a. Terminal segment of the principal leaves much larger than the lateral segments; flowers in spring and summer — 25. | |
| 24b. Terminal segment of the principal leaves equaling or smaller than the lateral ones (5-10 dm. high; pods very long and slender; flowers in summer) | Sisymbrium, Sisymbrium altissimum. |
| 25a. Flowers about 3 mm. wide; pods erect and closely appressed to the stem (3-9 dm. high; weed blooming in summer) (Hedge Mustard) — 26. | |
| 25b. Flowers about 7 mm. wide; pods spreading or ascending (3-6 dm. high; flowers in spring) (Winter Cress) — 27. | |
| 26a. Pods pubescent | Hedge Mustard, Sisymbrium officinale. |
| 26b. Pods glabrous | Hedge Mustard, Sisymbrium officinale var. leiocarpum. |
| 27a. Lateral leaf-segments 5-8 pairs on the principal leaves | Winter Cress, Barbarea verna. |
| 27b. Lateral leaf-segments 1-4 pairs on the principal leaves — 28. | |
| 28a. Flowers bright yellow, in racemes; pods spreading or ascending | Winter Cress, Barbarea vulgaris. |
| 28b. Flowers pale yellow, in corymb-like clusters; pods erect and somewhat appressed | Winter Cress, Barbarea stricta. |
| 29a. Principal stem-leaves compound or deeply lobed (the uppermost or bracteal leaves may be simple) — 30. | |
| 29b. Principal stem-leaves entire, dentate, serrate, or sometimes shallowly lobed or none (the basal leaves, at the surface of the ground, may be deeply lobed or compound) — 42. | |
| 30a. Leaves ternately divided or compound (2-5 dm. high; flowers in spring) (Toothwort) — 31. | |
| 30b. Leaves pinnately divided or compound — 33. | |
| 31a. Leaf-segments lanceolate or narrowly oblong | Toothwort, Dentaria laciniata. |
| 31b. Leaf-segments ovate or ovate-oblong — 32. | |
| 32a. Stem-leaves 2, opposite or nearly opposite | Toothwort, Dentaria diphylla. |
| 32b. Stem-leaves 2-5, alternate | Toothwort, Dentaria maxima. |
| 33a. Plants growing in water, or in mud near water (spring and summer) — 34. | |
| 33b. Plants of dry or moist soil — 35. | |
| 34a. Aerial leaves distinctly compound, with 3-11 leaflets | Water Cress, Radicula nasturtium-aquaticum. |
| 34b. Aerial leaves merely serrate to pinnatifid; the submerged leaves, if present, dissected | Lake Cress, Radicula aquatica. |
| 35a. Flowers 5 mm. broad, or less — 36. | |
| 35b. Flowers 6 mm. broad, or more — 39. | |
| 36a. Stem-leaves irregularly pinnatifid or lobed; pod about as broad as long (2-4 dm. high; flowers in summer) | Garden Cress, Lepidium sativum. |
| 36b. Stem-leaves distinctly pinnatifid, with 3-6 pairs of lateral segments (spring) (Bitter Cress) — 37. | |
| 37a. Leaves chiefly basal, pubescent on the upper side (1-3 dm. tall) | Bitter Cress, Cardamine hirsuta. |
| 37b. Stem-leaves conspicuous, glabrous on the upper side — 38. | |
| 38a. Plant of dry soil; flowers about 3 mm. wide (1-4 dm. high) | Bitter Cress, Cardamine parviflora. |
| 38b. Plant of moist or wet soil; flowers about 5 mm. wide (2-8 dm. high) | Bitter Cress, Cardamine pennsylvanica. |
| 39a. Leaves irregularly pinnatifid or lobed, not segmented into definitely paired divisions (coarse plants 4-8 dm. high; flowers in summer) — 40. | |
| 39b. Leaves deeply segmented into 3-10 pairs of divisions — 41. | |
| 40a. Flowers pink or white from the first | Radish, Raphanus sativus. |
| 40b. Flowers yellow at first, turning white with age | Wild Radish, Raphanus raphanistrum. |
| 41a. Flowers pink or white, appearing in spring (2-5 dm. high) | Cuckoo Flower, Cardamine pratensis. |
| 41b. Flowers yellowish or cream-color; a weed blooming in summer (5-10 dm. high) | Sisymbrium, Sisymbrium altissimum. |
| 42a. A fleshy, much-branched plant of the shores of the Great Lakes, with a pod transversely divided into two joints (2-3 dm. high; summer) | Sea Rocket, Cakile edentula. |
| 42b. Pod not transversely divided into two joints — 43. | |
| 43a. Pod short, its length not more than 3 times its diameter — 44. | |
| 43b. Pod long and slender, its length more than 3 times its diameter — 55. | |
| 44a. Pods not conspicuously flattened, thick and plump, about circular in cross-section (flowers in summer) — 45. | |
| 44b. Pods distinctly flat — 46. | |
| 45a. A plant escaped from cultivation in dry or moist soil, with very large basal leaves (5-10 dm. high) | Horse Radish, Radicula armoracia. |
| 45b. A plant of water or very wet soil, the largest leaves seldom more than 15 cm. long (1-5 dm. tall) | Lake Cress, Radicula aquatica. |
| 46a. Stem-leaves clasping the stem by an auricled base — 47. | |
| 46b. Stem-leaves sessile or petioled, not clasping, or none — 49. | |
| 47a. Stem and leaves glabrous or pubescent; pod very flat and circular, about 10 mm. wide (1-5 dm. tall; early summer) | Penny Cress, Thlaspi arvense. |
| 47b. Stem and leaves glabrous or pubescent; pod not more than 5 mm. wide (1-6 dm. high; spring and early summer) — 48. | |
| 48a. Pods broadly ovate | Field Cress, Lepidium campestre. |
| 48b. Pods triangular, or slightly indented at the apex | Shepherd's Purse, Capsella bursa-pastoris. |
| 49a. Pods about circular, or a very little longer than broad — 50. | |
| 49b. Pods ovoid or oblong, broadest near the middle, and distinctly longer than wide (Whitlow Grass) — 53. | |
| 50a. Leaves entire (1-3 dm. high; flowers in summer) | Yellow Alyssum, Alyssum alyssoides. |
| 50b. Leaves serrate (2-6 dm. high; flowers in summer) — 51. | |
| 51a. Stamens 6 | Garden Cress, Lepidium sativum. |
| 51b. Stamens 2 (Pepper Grass) — 52. | |
| 52a. Petals present | Pepper Grass, Lepidium virginicum. |
| 52b. Petals none | Pepper Grass, Lepidium apetalum. |
| 53a. Petals deeply 2-cleft (about 1 dm. high; early spring) | Whitlow Grass, Draba verna. |
| 53b. Petals entire or barely notched at the tip — 54. | |
| 54a. Leaves all or chiefly at or near the base (about 1 dm. high; spring) | Whitlow Grass, Draba caroliniana. |
| 54b. Stems leafy up to the flowers (1-5 dm. high; summer) | Whitlow Grass, Draba arabisans. |
| 55a. Stem-leaves cordate or sagittate at the base and sessile, forming a more or less clasping leaf (3-10 dm. high) (Rock Cress) — 56. | |
| 55b. Stem-leaves sessile or somewhat petioled, but not clasping — 63. | |
| 56a. Seeds in 2 rows in each cavity of the pod (early summer) — 57. | |
| 56b. Seeds in 1 row in each cavity of the pod — 59. | |
| 57a. Calyx pubescent; the pods reflexed | Rock Cress, Arabis holboellii. |
| 57b. Calyx glabrous; the pods spreading or ascending — 58. | |
| 58a. Basal leaves densely pubescent | Rock Cress, Arabis brachycarpa. |
| 58b. Basal leaves smooth or nearly so | Rock Cress, Arabis drummondii. |
| 59a. Petals conspicuous, about twice as long as the calyx, or longer; straight, erect, mostly unbranched plants — 60. | |
| 59b. Petals inconspicuous, equaling or but little longer than the calyx — 61. | |
| 60a. Pods 3-4 cm. long, ascending (summer) | Rock Cress, Arabis patens. |
| 60b. Pods 8-10 cm. long, recurved (late spring) | Rock Cress, Arabis laevigata. |
| 61a. Pods widely spreading; stem usually sparingly branched near the base (spring) | Rock Cress, Arabis dentata. |
| 61b. Pods erect or appressed; stem usually unbranched (summer) — 62. | |
| 62a. Stem-leaves and stem smooth and glaucous | Rock Cress, Arabis glabra. |
| 62b. Stem-leaves and stem almost always pubescent, and never glaucous | Rock Cress, Arabis hirsuta. |
| 63a. Principal stem-leaves 7-10 cm. long, or more — 64. | |
| 63b. Principal stem-leaves 2-5 cm. long — 65. | |
| 64a. Leaves lanceolate or oblong; flowers 10 mm. wide or less (3-7 dm. high; summer) | Rock Cress, Arabis canadensis. |
| 64b. Leaves ovate or ovate-lanceolate; flowers 15-20 mm. wide (5-8 dm. high; late spring and summer) | Dame's Rocket, Hesperis matronalis. |
| 65a. Basal leaves ovate to orbicular or cordate, not more than twice as long as broad (1-3 dm. high; spring) (Bitter Cress) — 66. | |
| 65b. Basal leaves oblong, lanceolate, or oblanceolate, at least 3 times as long as broad (1-3 dm. high) — 67. | |
| 66a. Flowers purple or rose color | Bitter Cress, Cardamine douglassii. |
| 66b. Flowers white | Bitter Cress, Cardamine bulbosa. |
| 67a. Basal leaves pinnatifid (spring and summer) | Rock Cress, Arabis lyrata. |
| 67b. Basal leaves entire or toothed — 68. | |
| 68a. Leaves narrowly oblanceolate; rare plant occurring from Mackinac northward (summer) | Rock Cress, Braya humilis. |
| 68b. Leaves obovate or oblong; an introduced weed (spring) | Mouse-ear Cress, Sisymbrium thalianum. |