BOSACEAE (ROSE FAMILY) 259 



the terminal one short-petiolulate; stipules large, ovate:, flowers few, in a, 

 close cyme: sepals and bractlets loosely silky, subequal, somewhat exceeded 

 by the obovate emarginate petals. — Subalpine; Colorado (Rydberg), Mon- 

 tana, and northwestward. 



21. PotentiUa nivea L. Sp. PI. 499. 1753. Stems tufted on the branched 

 caudex, which is brown-scaly with persistent petioles and stipules,. 1-2 dm. 

 high: leaves coarsely crenate, digitately ternate, glabrate or sparsely villous 

 above, densely white-tomentose beneath; the lower short-petioled; the upper 

 reduced; stipules ovate-lanceolate: cyme 2-6-flowered: calyx white-villous 

 or tomentose; the hnear-oblong bractlets shorter than the lanceolate acute 

 sepals: petals obcordate, barely longer than the sepals. — Not rare in alpine 

 stations of the Rocky Mountains. 



22. Potentilla uniflora Ledeb. Mem. Acad. Petersb. 5: 543. 1812. Stems 

 caespitose^rowded on the multicipital caudex, a few cm. high: leaves mostly 

 ttasal, 3-foliolate, silky or glabrate above, densely white-tomentose beneath; 

 leaflets broadly cuneate or rhombic-obovate, incisely cut from the apex, the 

 teeth coarse, oblong-lanceolate; stipules lanceolate: flowers usually sohtary 

 on the scapose stems: calyx grayish- vUlous; the sepals and bracts lanceolate, 

 subequal, only half as long as the obcordate petals. — Rare; in the higher 

 Rocky Mountains, north to the arctic seas. 



23. Potentilla i)imiatifida Dougl. Hook. Fl. Bor. Am. 1: 188. 1833. Stems 

 several from a thick pereimial root, erect, 3-4 dm. high, white silky-villous: 

 leaves pinnately 7-9-f oUolate, densely and finely silky above, white-tomentose 

 beneath; leaflets obovate, pectinately divided almost to the midrib; the seg- 

 ments liniear-oblong,, obtuse; stipules ovate-lanceolate, entire or toothed: 

 flowers in a congested cyme: calyx white-silky; the bractlets oblong-lanceolate, 

 shorter than the ovate sepals; petals obovate-truncate, with cuneate base, 

 barely exceeding the sepals. (P. pseudosericea Rydb. Monog. Pot. 1. c.) — 

 Frequent; the plains of Colorado to the far northwest. 



24. Potentilla pennsylvanica L. Mant. PI. 76. 1767. Stems single or several 

 from the same crown, erect, subtomentose, 3-5 dm. high: leaves puinately 

 7-15-foliolate, greenish and minutely pubescent above, grayish-tomentose 

 and veiny beneath; leaflets oblong, pinnately divided halfway to the midrib; 

 the pinnae scarcely re volute; stipules ovate in outline, pectinately divided: 

 flowers short-pediceled, ina dense cyme with erect branches: calyx, strigose- 

 tomentose; the acute sepals and bractlets subequal, nearly equaling the ob- 

 ovate, emarginate or truncate petals. — Infrequent, the following varieties 

 being far more common in the same range; extending from British America 

 along the high plains to Colorado. 



24a. Potentilla pennsylvanica strigosa Pursh, Fl. Am. Sept. 356. 1814. 

 Usually lower, pubescence mixed with some long strigose hairs: leaflets more 

 deeply divided, the segments narrowband re volute-margined: cyme short and 

 compact. — The most common form in our range and extending eastward to 

 the upper Missouri. 



246. Potentilla pennsylvanica arachnoidea Lehm. Stirp, Pug. 9: 41. 1851. 

 A reduced form with stems arachnoid-pubescent and the segments' of, the 

 leaflets short, silky-tufted at the apex. — Wyoming to Nev? Mexico and Ari- 

 zona. ^ . 



25. Potentilla atrovirens Rydb. Monog. Pot. 1, c. 95. Stemp few' from the 

 same crown, erect and rather stout, pilose, 2-4 dm. high: leaves dark green 

 and densely pilose on both sides, strongly veined, piimately 7-9-f oHolate; 

 leaflets obovate or oblanceolate, incisely and coarsely dentate, the segments 

 oblong: flowers numerous, in a narrow cyme, with erect branchlets: calyx 

 densely pilose; the bractlets and sepals subequal, exceeded bjr the cuneate- 

 obovate Dright yellow petals: carpels numerous; the style fusiform.-r-Infre- 

 qUent; Wyoming to Minnesota. 



■ 26. Potentilla virgulata A. Nels. Bull. Torr. Bot. Club 27:, 265; 1900. 

 Stems slenderly virgate, single from the one or two crowns of the thick root, 

 simple, glabrate, obscurely granulo-glandular, as are also the leaves, ,3-4 dm. 

 high: leaves few, erfict, pipna,tely,only 5-;7-foliolate, dark greeniabove, Ughter 



