36b. Stem-leaves distinctly pinnatifid, with 3-6 pairs of lateral segments (spring) (Bitter Cress) --37.

37a. Leaves chiefly basal, p.u.b.escent 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 (coa.r.s.e 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, Rapha.n.u.s sativus.=

40b. Flowers yellow at first, turning white with age =Wild Radish, Rapha.n.u.s 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 sh.o.r.es 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 p.u.b.escent; 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 p.u.b.escent; 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 Gra.s.s) --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 Gra.s.s) --52.

52a. Petals present =Pepper Gra.s.s, Lepidium virginic.u.m.=

52b. Petals none =Pepper Gra.s.s, Lepidium apetalum.=

53a. Petals deeply 2-cleft (about 1 dm. high; early spring) =Whitlow Gra.s.s, 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 Gra.s.s, Draba caroliniana.=

54b. Stems leafy up to the flowers (1-5 dm. high; summer) =Whitlow Gra.s.s, 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 p.u.b.escent; the pods reflexed =Rock Cress, Arabis holboellii.=

57b. Calyx glabrous; the pods spreading or ascending --58.

58a. Basal leaves densely p.u.b.escent =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.=