OF ARTS AND SCIENCES : MAT 13, 1873. 549 



Revision of the extra-tropical North American Species of the 

 Genus Potentilla (excluding Sibbaldia, Horkelia, and Ivesia). 

 — By Sereno Watson. 



The materials for this and the following revisions were the same as 

 for the last, namely, the collections belonging to Harvard and Columbia 

 Colleges, to the Philadelphia Academy, and to Professor Eaton. The 

 number of species has been considerably reduced, owing to a better 

 knowledge of some of the obscurer species, and especially to the less 

 weight which has been given to the distinction between pinnate and 

 digitate leaves and the number of leaflets, to differences in the amount 

 of pubescence, and in some species to the number of stamens. 



The genera Sibbaldia, Horkelia, and Ivesia, distinguished by minor 

 but apparently sufficient characters, are not included. The synonomy, 

 etc., of the common eastern species is limited mainly to references re- 

 specting their more western or northern range. 



Synopsis of Species. 



I. Styles fusiform ; carpels numerous, glabrous ; inflorescence terminal. 



* Style attached near the base of the ovary; disk thick- 



ened ; stamens 25 - 30 ; perennial herbs with glandu- 



lar-villous pubescence, pinnate leaves, and rather large 



white or yellow flowers. 

 Stout ; cyme strict and rather close ; leaflets 7-11; 



stamens mostly 30 1. P. arguta. 



Slender ; cyme loosely panicled ; leaflets 5 - 9 ; stamens 



mostly 25 2. P. glandidosa. 



* * Style terminal ; disk not thickened ; flowers sinall, 



yellow ; leaves pinnate or ternate. 

 t Annual or biennial ; leaflets incisely serrate, not white- 

 tomentose ; stamens 5-20 

 Stout, erect, hirsute ; cyme rather close, leafy ; leaves 



ternate; calyx large ; stamens 15, rarely 20 . . 3. P. Norvegica. 

 More slender and branched, softly villous ; cyme 

 loose, often diffuse, less leafy ; leaflets pinnately 5 

 or 3; calyx small ; petals minute; stamens 10-20 



(rarely 5) 4. P. rivalis. 



Subdecumbent, subvillous ; cyme loose, leafy ; leaflets 

 pinnately 5-11; stamens 20; achenia strongly 



gibbous on the ventral side 5. P. supina. 



1 1 Herbaceous perennials, more or less white-tomentose ; ■ 

 leaflets incisely pinnatifid ; bractlets and sepals 

 nearly equal ; stamens 20-25. 



