354 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



Key to the species 



1. Petals clear white, surpassing the sepals; leaves pinnate; plant perennial, 

 semiaquatic; leaflets entire or nearly so, the terminal one much the largest, 

 broadly ovate or suborbicular; pods cylindric or subclavate, 8 to 20 mm. 



long 1. R. NASTURTIUM- AQUATICUM. 



1. Petals yellow or whitish; leaves pinnatifid or sometimes pinnate; plants 



terrestrial, in moist soil (2). 



2. Sepals considerably shorter than the petals ; plants commonly perennial, with 



rootstocks; leaf segments mostly acute or acutish, the terminal one 



lanceolate or oblong; pods seldom less than 3 times as long as wide, 



acute or acutish at apex; stigma much thicker than the style (3). 



3. Leaves often pinnate, the segments mostly toothed, cleft, or laciniate; 



inflorescence and pods glabrous; style not more than 1 mm. long; pods 



slender; seeds often in one row 2. R. sylvestris. 



3. Leaves pinnatifid, the segments entire or nearly so; inflorescence and pods 



scurfy-papillate; style more than 1 mm. long; pods rather thick, 



usually curved; seeds in two rows 3. R. sinuata. 



2. Sepals not or only slightly shorter than the petals (except sometimes in 

 II. curvisiliqua) ; plants commonly annual (4). 



4. Pods very slender, linear, more or less curved, often 1 cm. long or longer, 



acute or acutish at apex; stigma very small, not thicker than the very 

 short style, or sessile; leaf segments commonly acute. 



4. R. CURVISILIQUA. 



4. Pods thick, straight or nearly so, usually much less than 1 cm. long, very 



obtuse or truncate at apex (5). 



5. Pedicels 2 to 4 mm. long, mostly longer than the globose pods; plant 



low, diffuse, glabrous or very sparsely pilose; leaf segments obtuse. 



5. R. SPHAEROCARPA. 



5. Pedicels mostly 4 mm. long or longer; pods longer than wide (6). 



6. Stems villous or hirsutulous, commonly sparsely so; pods not more 

 than twice as long as wide, ovoid or ellipsoid, mostly shorter than 

 the pedicels; stigma scarcely thicker than the style. 



6. R. HISPIDA. 



6. Stems glabrous or very nearly so; pods usually more than twice as 



long as wide, cylindric or ovoid-cylindric, mostly longer than the 



pedicels (7). 



7. Stigma thicker than the style, distinctly 2-lobed; leaf segments 



numerous, often acutish 7. R. islandica. 



7. Stigma not or scarcely thicker than the style, entire or very nearly 

 so; leaf segments few, obtuse 8. R. obtusa. 



1. Rorippa nasturtium -aquaticum (L.) Schinz and ThelL, Fl. Schweiz, 



ed. 3, 240. 1909. 



Sisymbrium nasturtium-aquaticum L., Sp. PL 657. 1753. 

 Radicula nasturtium-aquaticum Britten and Rendle, Jour. Bot. 

 [London] 14:99. 1907. 



Apache County to Coconino County, south to Graham, Pinal, and 

 Pima Counties, 1,300 to 7,000 feet, springs, brooks, and ponds, April 

 to July. Naturalized throughout temperate North America, from 

 Europe. 



Watercress, sometimes cultivated for salads and garnishings. 



2. Rorippa sylvestris (L.) Besser, Enum. PI. 27. 1821. 



Sisymbrium sylvestre L., Sp. PL 657. 1753. 



Radicula sylvestris Druce, Ann. Nat. Hist. 1906: 219. 1906. 



Oak Creek, Coconino County (Fulton 9666), Fort Huachuca, 

 Cochise County (Patzky in 1890). Yellowcress, extensively natural- 

 ized in North America, from Europe. 



I 



