In mud at edge of lakes and ponds, and other wet places, in Ariz. (Coconino, 

 Navajo, Pinal and Yavapai cos.), June-Sept.; Mont, and Wyo., s. to Ariz, and 

 Calif. 



7. Rorippa obtusa (Nutt.) Britt. 



Diffusely branched glabrous annual with erect to somewhat decumbent stems 

 1.5-4 dm. long; leaves oblong-lanceolate, 2-6 cm. long, shallowly sinuately lobed 

 to pinnatifid with the obovate rounded segments sinuately lobed to entire; pedicels 

 ascending to spreading, 2-4 (-7) mm. long, usually shorter than the fruit; sepals 

 deciduous shortly after anthesis; petals pale-yellow, spatulate, 1-2 mm. long; 

 siliques ovoid to oblong-lanceolate, 4-8 mm. long, 2-2.5 mm. broad; style 0.5-1 

 mm. long, the small stigma entire; seeds about 0.5 mm. long, minutely alveolate- 

 papillate. 



Wet soil along streams and ditches, and in wet meadows, rather widespread in 

 mts. of N. M. and Ariz., June-Sept.; Mich, and Mo., w. to B.C., N.M., Ariz, 

 and Calif. 



8. Rorippa teres (Michx.) Stuckey. Fig. 474. 



Annual or biennial; stems 1-3 dm. long, erect to decumbent, branched; sparsely 

 pubescent with vesicular trichomes, rarely glabrous; leaves oblong to oblanceolate, 

 deeply pinnatifid and with the remote segments obtusely toothed, petiolate; 

 racemes terminal and axillary, densely flowered; petals minute, about 1 mm. long, 

 yellow; pedicels spreading, 2-5 mm. long; siliques linear-oblong, 1-1.5 cm. long, 

 straight or slightly curved; styles evident, about 1 mm. long; seeds numerous, 

 plump, slightly longer than broad, about 0.5 mm. long. R. Walteri (Ell.) Mohr. 



Wet fields, lakes, ponds and stream margins and swamp land, s.-cen. Okla. 

 (Marshall Co.) and e. and s.w. Tex., Dec-May; S.C. and Fla. to Okla. and C. A. 



9. Rorippa ramosa Roll. 



Perennial; stems numerous, decumbent, highly branched, sparsely pubescent 

 with vesicular trichomes, 3-6 dm. long; leaves numerous, sessile, auriculate, 

 oblong to broadly lanceolate, pinnately lobed, 3-5 cm. long, 5-12 mm. wide; in- 

 florescences short, mostly less than 5 cm. long; petals pale-yellow, 2.5-3 mm. 

 long; pedicels widely spreading to ascending, 3-5 mm. long; siliques divaricately 

 spreading to erect, oblong to lanceolate in outline, plump, 6-10 mm. long; valves 

 densely covered with vesicular trichomes along their margins; styles 1.5-2.5 mm. 

 long; seeds plump, cordiform, about 1.5 mm. in diameter. 



Floodplains and intermittent stream beds. Big Bend region near the Rio Grande 

 in w. Tex., Mar.-May; also Coah. to Dgo. 



8. Armoracia Gaertn. 



Three species in Eurasia and one species in North America. The ground 

 thick roots of A. rusticana (Lam.) Gaertn., Mey. & Scherb. is the condiment, 

 horse-radish. 



1. Armoracia aquatica (Eat.) Wieg. Lake cress. Fig. 475. 



Plant weak from a slender rootstock, to about 6 dm. tall; stems commonly 

 submersed; submersed leaves repeatedly pinnately dissected into numerous fili- 

 form segments; emersed leaves (if present) lancolate to narrowly oblong, 3-7 cm. 

 long, finely to coarsely dentate; petals 6-8 mm. long; mature pedicels divaricate, 

 about 1 cm. long; fruits rarely perfected, ellipsoid or somewhat obovoid, 5-8 mm. 

 long, 1 -celled; persistent style slender, 2-4 mm. long. 



In quiet water of lakes and streams, and on muddy shores in e. Okla. (Cherokee 

 and McCurtain cos.) and e. Tex. (Tyler Co.), Apr .-July; Que. to Ont. and Minn., 

 s. to Fla. and Tex. 



979 



