24 MEMOIRS FROM THE DEPARTMENT OF BOTANY OF COLUMBIA UNIVERSITY 



§5. ARGENTEAE. 



Perennials, with leafy stems and more or less leafy many-fiowered cymes. Flowers 

 small. Petals slightly exceeding the sepals, yellow, obovate and slightly emarginate. 

 Stamens 20, with rather short filaments. Pistils numerous ; style short, rather stout, but 

 neither thickened nor glandular at the base. 



A group of European and Asiatic origin, but P. argentea common also in eastern 

 North America. 



Leaves green on both sides. 21. P. intermedia. 



Leaves grayish silky and slightly tomentose beneath. 22. P. inclinata. 



Leaves white-tomentose beneath. 



Teeth of the leaves ovate, margin not revolute ; fruiting calyx 5-7 mm. in 



diameter. 2.3. P. collina. 



Teeth of the leaves oblong or linear, margin revolute ; fruiting calyx 5 mm. 



in diameter or less. 24. P. argentea. 



§ 6. CONCINNAE. 



Plants perennial with a more or less thickened caudex ; stems generally several, low, 

 spreading or at last prostrate. Leaves digitately 5-7-foliolate, silky above, more or less 

 tomentose beneath. Cymes few-flowered. Petals yellow, broadly obovate to cuneate, 

 truncate or emarginate, a little exceeding the sepals. Style filiform but rather short. 



A small group containing only four American species. It is nearest related to the 

 Niveae, Aureae and Subviscosae differing mainly from the first by the more numerous 

 leaflets and from the last two by the tomentum. (P. qioinquefolia with the terminal leaf- 

 lets petiolate may be sought in this group.) 



Leaves densely tomentose beneath. 



Leaflets obovate or cuneate, deeply toothed or incised ; sepals and bract- 

 lets ovate or oblong. 25. P. concinna. 

 Leaflets oblanceolate, with small upwardly directed teeth ; sepals and 



bractlets narrowly lanceolate. 26. P. oblanceolata. 



Leaflets oblong with entire margins, only 3-toothed (seldom 5-toothed) 



at the very apex. 27. P. hicrenata. 



Leaves densely silvery-silky on both sides, only slightly tomentose beneath. 28. P. condnnaeformis. 



§ 7. SUBVISCOSAE. 

 Perennials, with a deep thick root. Stems many, short, spreading with divergent 

 branches. Leaves silky or hirsute, not at all tomentose. Petals yellow, obcordate and 

 often inchned to be slightly unguiculate, exceeding the calyx. Bractlets and sepals in- 



