OF ARTS AND SCIENCES : MAY 13, 1873. 551 



Flowers 3 - 6 ; bractlets much shorter ; Western 23. P. Grayi. 



Flowers solitary ; bractlets and sepals equal, ob- 

 tuse ; very dwarf, villous ; White Mts. . . 24. P. frigida. 

 Leaflets roundish, 2 - 3-lobed and crenate ; glan- 



dular-puberulent ; Rocky Mts. ... 25. P. brevifolia. 

 * * Style terminal or medial ; carpels glabrous ; disk thick- 

 ened or glandular; stamens 20; smooth or 

 smoothish herbaceous perennials, with large pur- 

 ple or yellow flowers. 

 Style attached to the middle of the ovary ; flowers 



purple ; leaves pinnately 5 - 7-foliolate . . 26. P. palustris. 



Style terminal; flowers purple; leaves digitately 



5 - 7-foliolate ; New Mexico . . . 27. P. Thurberi. 



Style attached below the apex ; flowers yellow ; leaf- 

 lets 3, 2- 3-parted ; arctic, dwarf . ... 28. P.biflora. 

 * * * Style attached below the middle ; carpels and recepta- 

 cle densely villous ; woody perennials. 

 Shrubby, erect, much branched ; leaves pinnate ; 



leaflets 5-7, entire 29. P.Jruticosa. 



Woody only at base, low ; leaflets 3, toothed at the 



apex ; flowers white 30. P. tridentata. 



III. Styles filiform ; peduncles axillary, solitary, 1-flowered ; carpels glabrous ; 

 stems creeping or decumbent ; herbaceous perennials. 



Style attached to the middle of the ovary ; leaves pin- 

 nately 7 -21-foliolate '. 31. P. Anserina. 



Style attached below the apex; leaves apparently qui- 



nate 32. P. Canadensis. 



Style attached below the apex ; leaves ternate or quinate ; 



sepals and petals usually 4 ..... 33. P. nemoralis. 



I. Styles thickened and glandular toward the base ; carpels glabrous, 

 numerous, sessile ; inflorescence cymose. — Spec. 1 — 8. 



* Style attached below the middle of the ovary ; disk thickened and 

 pentagonal; stamens 25-30, rarely twenty, in one row on the 

 margin, of the disk; herbaceous perennials, with pinnate leaves; 

 pubescence glandular-villous. 



1. P. arguta, Pursh. Stems erect, usually stout, 1-4° high, sim- 

 ple below; pubescence spreading;, stipules ovate, acute, entire or 

 incised ; radical leaves 7 - 11-foliolate, 4—12' long, usually long-petioled ; 

 leaflets rounded, ovate, or subrhomboidal, incised or doubly serrate, 

 smoother on the upper surface, the terminal one 1-3' long ; cyme 

 usually crowded, with strict pedicels becoming rigid ; calyx densely 

 pubescent, the acute sepals 3 - 4" (becoming 5") long, bractlets much 



