558 PROCEEDINGS OF THE AMERICAN ACADEMY 



16. P. argentea, L. Densely white-tomentose throughout and 

 subvillous, excepting the smooth green upper surface of the leaves ; 

 stems short, ascending or decumbent ; stipules lanceolate, entire, or 

 toothed; leaflets 5, cuneate-obovate to narrowly oblanceolate, \- 1' 

 long, coarsely incised from above the base or only few-toothed towards 

 the apex, the margin mostly revolute ; flowers few to many, in a close 

 or loosely panicled cyme, the pedicels short or often slender and elon- 

 gated ; sepals and bractlets equal, acute ; petals obovate, 2" long or 

 less, equalling the calyx ; achenia very numerous, dotted ; style short 

 but rather slender. — New England to Canada and Michigan. 



17. P. humifusa, Nutt. (P. concinna, Rich.) Densely white-tomen- 

 tose and silky-villous ; stems decumbent, 2-4' long, slender ; leaflets 5> 

 cuneate-oblong, 6-9" long, green and appressed-silky above, only the 

 rounded or truncate apex serrate with 3-5 teeth ; flowers 8 — 5, on 

 slender pedicels ; bractlets narrow, shorter than the acute sepals ; 

 petals 2 — 3" long, obcordate, exceeding the calyx ; carpels 15 - 20. — 

 From the Saskatchewan to the Rocky Mts. of Colorado. 



fft Leaves ternate (quinate in P. maculata, and very rarely qui- 

 nate or pinnately 5-foliolate in P. nivea) ; low, arctic or alpine, 

 sparingly villous or subglabrous (densely tomentose or villous in 

 P. nivea and fragiformis) ; flowers few, in a loose cyme, or soli- 

 tary, the obcordate petals exceeding the calyx ; carpels 10 - 40. 



18. P. nivea, L. (P. Vahliana, Lehm.) Pubescence silky-villous, 

 often abundant, densely white-tomentose on the under .side of the 

 leaves and sometimes upon the calyx; stems 2-12' high; leaflets 

 cuneate-obovate or -oblong, 3 - 8" long, coarsely incised-serrate or pin- 

 natifid, the terminal one sessile or petiolulate ; flowers few or solitary 

 on slender pedicels ; bractlets acute or acutish, shorter than the sepals ; 

 petals 2 - 4" long ; carpels few or many. — Labrador, Greenland, 

 throughout Arctic America and in the Rocky Mts. southward to Colo- 

 rado and the Uintas. P. Vahliana seems to be but a reduced large- 

 flowered form. The var. concolor, R, Br., without tomentum, is to be 

 referred to P. emarginata, having the peculiar calyx of that species. 

 Most Labrador and some Greenland specimens, which have been con- 

 sidered P. nivea, are for the same reason rather to be carried to emar- 

 ginata, though more or less tomentose. Some Rocky Mountain 

 specimens so simulate reduced forms of P. Hippiana or gracilis, that, 

 but for their ternate leaves, they might as well be so considered. The 

 following variety makes the connection yet more close. 



