2(1). Plant shrubby; ovaries and achenes strongly hirsute 2. P. fruticosa. 



2. Plant herbaceous" ovaries and achenes glabrous (3) 



3(2). Leaves palmately (or digitately) lobed or divided (4) 



3. Leaves pinnately lobed or divided (8) 



4(3). Perennials with usually well-developed rootstocks; leaves often white- 

 tomentose on the lower surface; stamens 20 to 40 (5) 



4. Annuals, biennials or sometimes short-lived perennials but without definite 



rootstocks; leaves never white-tomentose on lower surface; stamens 

 5 to 20 (6) 



5(4). Plant 1.5-4.5 dm. tall, alpine or subalpine; leaflets only occasionally more 

 than 3.5 cm. long, typically greenish or about equally grayish- 

 sericeous on both surfaces; anthers 0.4-0.6 mm. long... 



8. P. diversifolia. 



5. Plants to 8 dm. tall, in lowlands to medium elevations in mountains; leaflets 



mostly much more than 3.5 cm. long, the lower surface usually 

 tomentose and much paler than upper surface; anthers 0.8-1.3 mm. 

 long 9. P. gracilis. 



6(4). Lower leaves 5-foliolate or ternate with the lateral leaflets 2-cleft to near 

 the base; stamens 5 4. P. pentandra. 



6. Leaves 3-foliolate (7) 



7(6). Petals about half as long as sepals; hypanthium in fruit 5 mm. wide or 

 less; stamens about 10 5. P. biennis. 



7. Petals equaling the sepals or nearly so; hypanthium in fruit about 7 mm. wide; 



stamens 15 to 20 3. P. norvegica. 



8(3). Annuals, biennials or sometimes short-lived perennials but without definite 

 rootstocks; leaves never white-tomentose on lower surface; stamens 

 5 to 20 (9) 



8. Perennials with usually well-developed rootstocks; leaves often white-tomentose 



on the lower surface; stamens 20 to 40 (10) 



9(8). Principal leaves below inflorescence typically 3-foliolate; achenes smooth 

 and without ventral protuberances 6. P. rivalis. 



9. Principal leaves below inflorescence with 5 to several leaflets; achenes longi- 



tudinally ribbed and with a corky protuberance on ventral surface 

 7. P. paradoxa. 



10(8). Basal leaves bipinnately lobed 12. P. plattensis. 



10. Basal leaves simply pinnate (11) 



11(10). Flowers single on naked peduncles 13. P. Anserina. 



11. Flowers usually several on more or less leafy flowering stems (12) 



12(11). Style slenderly fusiform, attached below middle of ovary; stamens 25 

 or more (13) 



12. Style usually tapered from base or filiform, or attached near top of ovary; 



stamens 20 (14) 



13(12). Cymes narrow and strict, the lateral branches almost erect; sepals 5-9 

 mm. long at anthesis; herbage conspicuously villous.... 1 1. P. arguta. 



13. Cymes usually open to diffuse, the lateral branches not tightly appressed; 



sepals 4-6 mm. long at anthesis; herbage not conspicuously villous 

 10. P. glandulosa. 



14(12). Leaves silky-strigose to glabrate on lower surface, the two surfaces 



essentially concolorous; anthers mostly 0.4-0.6 mm. long 



8. P. diversifolia. 



14. Leaves white-tomentose on lower surface, the upper surface dark green; 



anthers mostly 0.8-1.3 mm. long 9. P. gracilis. 



1022 



