4(3). Siliques short and thick, globose or ovoid to broadly oblong and obtuse (5) 



4. Siliques elongated, terete (6) 



5(4). Siliques globose, about 2 mm. in diameter 4. R. sphaerocarpa. 



5. Siliques ovoid to broadly oblong, obtuse, usually more than 3 mm. long 



5. R. islandica. 



6(4). Plants glabrous or (if with indument) the trichomes simple and pointed (7) 



6. Vesicular trichomes present on stems, foliage or siliques (8) 



7(6). Pods usually strongly curved, 8 cm. long or more; leaf segments linear to 



oblong, mostly acute; style stout, not over 0.5 mm. long 



6. R. curvisiliqua. 



1. Pods not curved, 4-8 cm. long; leaf segments obovate or rounded; style 

 slender, 1-2 mm. long 7. R. obtusa. 



8(6). Leaf segments deeply dentate; lower leaves pinnatifid; cauline leaves 

 petiolate 8. R. teres. 



8. Leaf segments entire; lower leaves merely lobed; cauline leaves sessile 



9. R. ramosa. 



1. Rorippa Nasturtium-aquaticum (L.) Hayek. Water-cress. Fig. 472. 



Aquatic to semi-aquatic perennial, glabrous; stem's floating, creeping or ascend- 

 ing, rooting at the nodes; leaves pinnately compound with 3 to 9 segments; 

 leaflets ovate to oval, terminal larger than the lateral, somewhat fleshy; petals 

 3-4 mm. long; fruiting pedicels divaricate, 8-12 mm. long; fruit 1-2 cm. long, 

 ellipsoid, spreading or curved upward; style about 1 mm. long; seeds about 1 mm. 

 long, plump, nearly orbicular. Nasturtium officinale R. Br. 



In clear water of slow-running streams and on stream margins, in and about 

 cold springs, throughout most of our region, Mar .-July; widely dispersed as an 

 introd. from Eur. 



This is the common water cress used in salads. 



2. Rorippa sinuata (Nutt.) Hitchc. Fig. 473. 



Perennial with creeping rhizomes; stems 2-4 dm. tall, glabrous, highly 

 branched, erect to decumbent; leaves oblong to oblanceolate, deeply pinnatifid, 

 the segments entire or nearly so; petals obovate, not differentiated into blade 

 and claw, exceeding sepals; pedicels slender, 6-10 mm. long, spreading; siliques 

 curved upward, 8-14 mm. long, about 2 mm. wide; seeds angular, plump, 0.7-0.8 

 mm. long. 



Moist gravel along streams, seepy stream banks, borders of lakes and marshes, 

 also waste places generally, in Okla. {Waterfall), n. and w. Tex. and N. M. (Mora 

 Co.), Apr.-July; 111. and cen. Can. to Wash., Nev. and N. M. 



3. Rorippa sessiliflora (Nutt.) Hitchc. 



Annual or biennial with a taproot; stems erect, branched, 2-5 dm. tall, 

 glabrous; leaves petiolate, oblanceolate, dentate; flowers in terminal and lateral 

 racemes, small; sepals yellowish; petals absent or very rarely a petal may be 

 seen in one or two flowers of a plant; pedicels less than 1 mm. long; siliques 

 sessile or nearly so, terete to slightly compressed parallel to septum, oblong, 

 6-10 mm. long; styles less than 1 mm. long; seeds numerous, cordiform, plump, 

 0.4-0.6 mm. long. 



Wet land, river floodplains and along sluggish stream margins or around ponds, 

 in n.-cen. Okla. (Alfalfa Co.) and n. and e. Tex., Apr.-Aug.; Tex. and La. to 

 Va., Ind. and Minn. 



974 



