122 ROSACE.\E 



Leaflets thin, sparlnglj- tomentose beneath; teeth lanceolate. 



61. P. viridior. 

 Leaves gresn beneath, only slightly tomentiilose when young: pubescence of the 



stems and petioles spreading. 62. P. ambigens. 



XIV. MULTUUGAE. 



Pedicels at least in fruit arcuate-spreading; stems usually diffuse or spreading; leaflets 

 pinnately divided, with several or many, oblong or lanceolate divisions. 



63. P. platlensis. 

 Pedicels erect or ascending, straight; stem erect or ascending. 



Leaflets dissected to near the midrib. 



Stem and mature leaves glabrate; leaflets cuneate, cleft above the middle into 

 oblong or ovate divisions. 

 Stem 1-3 dm. high ; leaflets elongate-cuneate, with oblong divisions. 



64. P. Nelsoniana. 

 Stem about 1 dm. high; leaflets short-cuneate, merely toothed at the apex. 



65. P. decurrens. 

 Stem and mature leaves more or less hairy; leaflets obovate, at least the uppej 



pinnatisect. 

 Divisions of the leaflets long, narrowly linear; stem 2-3 dm. high; leaflet-; 



many. 66. P. wyomingensis. 



Divisions of the leaflets oblong or oblanceolate; stem less than 2 dm. high; 

 leaflets few. 67. P. oeina. 



Leaflets not dissected to near the midrib. 

 Leaves not densely grayish-strigose. 



Sepals ovate or lance-ovate; bractlets lanceolate or oblong. 



Stem about 1 dm. high; leaflets 1 cm. long or less, toothed only at the apex. 



65. P. decurrens. 

 Stem 2-4 dm. high; leaflets more than 2 cm. long. 68. P. Drummondii. 

 Sepals linear -lanceolate, acuminate; bractlets linear-subulate. 



54. P. rupincola. 

 Leaves denselv grayish-strigose or silky. 



Stem 1—1 dm. liigh. ascending or decumbent; leaflets ctmeate or linear-oblong, 



conduplicate, toothed at the apex only. 69. P. crinita. 



Stem stout, 6-7 dm. high; leaflets obovate-oblong, coarsely serrate. 



62. P. ambigens. 



XV. MULTIFIDAE. 



Pubescence of the under side of the leaves silvery-white. 



Petioles and lower part of the stem silky villous with spreading hairs. 



70. P. paucijuga. 

 Petioles and stem tomentulose and silky strigose. 



Segments of the leaflets Imear or linear-oblong; branches of the inflorescence 

 usually short and ascending. 

 Leaflets usually wliite on both sides; petals and sepals 4-6 mm. long. 



Stem decumbent or ascending, 0.5-1 dm. high; leaflets 2 or 3 rather approx- 

 imate pairs. 71. P. pseudosericea. 

 Stem erect, 3-5 dm. liigh; leaflets 3-7 usually rather remote pairs. 



72. P. bipinnatifida. 

 Leaflets green above; petals and sepals about 3 mm. long. 



73. P. virgulata. 

 Segments of the leaflets lanceolate or oblong, usually green above; branches of 



the inflorescence long and erect. 74. P. platyloba. 



Pubescence of the under side of the leaves grayish. 

 Petioles and stem appressed-pubescent. 



Segments of the leaflets narrowly linear; petals and sepals about 3 mm. long. 



73. P. rirgulata. 

 Segments of the leaflets ovate, lanceolate, or oblong; petals and sepals 4-6 mm. 

 long. 

 Leaves glandular-pruinose above and sometimes with scattered long hairs. 



75. P. glabrella. 

 Leaves short-strigose above. 



Margins of the leaf-segments not revolute. 76. P. pennsijlranica. 



^Margins of the leaf-segments revolute. 77. P. arachnoidea. 



Petioles and stem with spreading hairs. 



Flowers distinctly pedicelled: upper leaflets of the basal leaves with 9-13 segments; 

 pubescence of the stem and petioles long. 

 Plant dark green; leaves scarcely paler beneath. 78. P. atrmirens. 



Plant not dark green; leaves decidedly paler beneath. 79. P. strigo.sa. 

 Flowers usually subsessile, densely conglomerate; upper leaflets of the basal leaves 

 with 15-21" segments; pubescence of the stem short and dense. 



80. P. lasiodonta. 



13. ARGENTINA Lam. Silver-weed, Goose Tansy. 



Achenes corky, with a deep groove; stem and petiole and rachis of the leaves densely 

 pubRscent, with at first ascending and later spreading hairs. 

 Leaves silvery on both sides. 1. ^1. argentea. 



Leaves green and glabrate above. 2. A. Anserina. 



Achenes not corky, without a groove; stem and petiole and the rachis of the leaves gla- 

 brous or slightly appressed-hairy and glabrate; hypanthium acute at the base. 



3. A. subarctica. 



