122 ROSACEAE 



Leaflets thin, sparingly tomentose beneath; teeth lanceolate. 



61. P. viridior. 

 Leaves green beneath, only slightly tomentulose when young; pubescence of the 



stems and petioles spreading. 62. P. ambigens. 



XIV. MULTIJDGAE. 



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. plattensis. 

 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. NeUoniana. 

 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 



^innatisect. 

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



many. 66. P. wyomingensis. 



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

 leaflets few. 67. P. ovina. 



Leaflets not dissected to near the midrib. 

 Leaves not densely grayish-strigose. 



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



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 densely grayish-strigose or silky. 



Stem 1-4 dm. high, ascending or decumbent; leaflets cuneate or linear-oblong, 



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



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



62. P. ambigens. 



XV. MULTIPIDAE. 



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



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



70. P. paucijuga. 

 Petioles and stem tomentulose and silky strigose. 



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

 usually short and ascending. 

 Leaflets usually white on both sides; petals and sepals 4^6 mm. long. 



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

 imate pairs. 71. P. pseudosericea. 

 Stem erect, 3-5 dm. high; 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. virgulata. 



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

 long. 

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



, ^ ^ . , 75. P. glabrella. 



Leaves short-strigose above. 



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



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. atrovirens. 



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

 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 Tanst. 



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

 pubescent, with at first ascending and later spreading hairs. 

 Leaves silvery on both sides. I. a 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; hypauthium acute at the base. 



3. A. subarctica. 



