Cruciferae, the Mustard Family
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. |