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, Badicnla 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 cir- 

 cular, 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, Capselia bnrsa-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, jMyssum 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 Yirginicum. 



52b. Petals none Pepper Grass, Lepidium apetalurn. 



53a. Petals deeply 2-cleft (about 1 dm. high; early spring) 



Whitlow Grass, Draba yerna. 

 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, form- 

 ing 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 sum- 

 mer) 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. 



