ROSE FAMILY 421 



grayish or white beneath, dissected into narrowly linear divisions, with revolute 

 margins; cyme congested; sepals lanceolate, 2-3 mm. long; petals small, orbicu- 

 lar, about 4 mm. long, slightly emarginate. Wet grassy flats: Wyo. Utah- 

 Alaska. Submont. Jl. 



74. P. platyloba Rydb. Stems several, erect or ascending, 3-5 dm. high, 

 pubescent with white appressed hairs; leaves pinnate, usually with but two pairs 

 of leaflets; leaflets obovate, 2-6 cm. long, greenish and silky-strigose above, 

 white-tomentose beneath, cleft into broad lanceolate or oblong divisions; stem- 

 leaves short-petioled and often subdigitate; sepals ovate, acute; petals about 

 equalling the sepals, obovate. Plains: Hudson Bay Colo. Alta. Plain- 

 Mont. Je-S. 



75. P. glabrella Rydb. Stem erect and strict, rather low, 1-2 dm. high, 

 glabrate or sparingly pubescent; leaves pinnate, with 5-11 rather approximate 

 leaflets, glabrate or glandular-pruinose, sparingly hairy on the veins and margins; 

 leaflets obovate to oblanceolate, the lower ones smaller, very deeply dissected 

 into oblong, acute or obtuse segments; sepals broadly ovate, rather strongly 

 veined, about 5 mm. long; petals obovate, about equalling the sepals. P. penn- 

 sylvanica glabrata S. Wats. Mountains: Sask. Alta. Wyo. Submont. Jl- 

 Au. 



76. P. pennsylvanica L. Stem generally erect, strict, 4-8 dm. high, more 

 or less appressed-pubescent and tomentulose; leaves pinnate, with 7-15^ leaflets, 

 grayish tomentose and veiny beneath, short-strigose and green above; leaflets 

 gradually reduced downward, often somewhat decurrent, oblong or oblanceolate 

 in outline, divided halfway to the midrib into oblong divisions; sepals ovate- 

 triangular, acute, usually not prominently veiny, about 5 mm. long; petals 

 obovate, cuneate, slightly emarginate or truncate, about 6 mm. long. Plains: 

 Hudson Bay Yukon Colo. Plain Mont. Jl. 



77. P. arachnoidea Dougl. Stems densely pubescent, with partly short, 

 partly longer appressed hairs, 1-3 dm. high, erect, strict; basal leaves pinnate, 

 with 9-13 leaflets; leaflets obovate or oblanceolate, 1-3 cm. long, green and 

 rather densely short-puberulent above, grayish tomentose and silky on the veins 

 beneath, deeply cleft into lanceolate or linear divisions, with revolute margins; 

 inflorescence congested; sepals lance-ovate; petals broadly obovate, emarginate, 

 4-5 mm. long. P. pennsylvanica arachnoidea Lehm. Dry plains and hills: 

 N.M. Ariz. Mont. Plain Submont. Jl-Au. 



78. P. atrovirens Rydb. Stem stout, 2-3 dm. high, with erect branches, 

 dark colored, densely pilose; leaves very dark green, densely pilose on both 

 sides, strongly veined, pinnate, with 7-9 leaflets; these obovate to oblanceolate, 

 coarsely dissected about halfway to the midrib into oblong segments; sepals 

 and bractlets subequal, about 5 mm. long, ovate, exceeded by the cuneate-obovate 

 bright yellow petals. Plains: Minn. Wyo. Colo. Plain. Je-Jl. 



79. P. strigosa Pall. Stems 1-4 dm. high, densely puberulent and with 

 long spreading hairs; basal leaves pinnate, with 7-11 leaflets; leaflets obovate 

 or oblanceolate, 1-5 cm. long, densely silky-pubescent, but yellowish green 

 above, densely grayish-tomentose and silky beneath, deeply cleft into lanceolate 

 or linear, revolute divisions; sepals ovate, rlightly longer, strongly ribbed; petals 

 obovate or orbicular, about equalling the sepals. Plains: Hudson Bay Kans. 

 N.M. B.C. Plain Submont. Je-Au. 



80. P. lasiodonta Rydb. Stem strict, 3-4 dm. high, densely pubescent, 

 with short spreading pubescence; basal leaves pinnate, with 11-15 leaflets; leaf- 

 lets oblong, 1-4 cm. long, green and densely short-pubescent, almost velvety 

 above, grayish tomentose beneath, deeply serrate; sepals ovate, acute, strongly 

 ribbed, about 6 mm. long; petals rounded-obovate, slightly if at all exceeding 

 the sepals. Plains: Sask. S.D. Alta. Plain. Jl-Au. 



13. ARGENTINA Lam. SILVER-WEED, GOOSE TANSY. 



Perennial herbs, with slender prostrate stolons. Leaves interruptedly pin- 

 nate, with many leaflets. Flowers solitary in the axils of small leaves or scales 



