MEMOIES FROM THE DEPARTMENT OF BOTANY OF COLUMBIA UNIVERSITY 33 



P. Thurberi diflfers from the other purple-flowered American species by its green, 

 often glabrate and thinner leaves, the teeth of which are much broader and rounder 

 than in P. atrorubens and much deeper than in P. Haematochrus. It seems to be a com- 

 paratively rare plant, growing in New Mexico, California and Arizona and probably 

 in northern Mexico. 



New Mexico: Thurber, No. 1107, 1851; Dr. Henry, 1854; Dr. Bigelow (Mex. 

 Bound. Surv.), No. 347, 1851 ; E. L. Greene, 1880; E. Palmer, 1869; F. H. Snow, No. 

 2290, 1884. 



Arizona: J. T. Rothrock, No. 310, 1874; Lemmon, 1881 ; C. G. Pringle, 1884; E. 

 A. Mearns, 1885 (depauperate); Wooton, 1895; J. W. Tourney, 1896; Dr. Kunze, 1896. 



California: Parry, No. 22. 



2. Potentilla atrorubens Rydberg. 



Potentilla atrorubens Rydberg, Bull. Torr. Bot. Clab, 24 : 11. 1897. 



Potentilla Thurberi Rothrock, Wheeler Surv. 4: 113, mainly. 1878. Britton, Trans. 

 N. Y. Acad. Sci. 8 : 66. 



Illustrations : Bull. Torr. Bot. Club, 24 : pi. 288. Plate 3, f. 1 and 2; dissection 

 of flower,/. 3; stamens,/. 4; pistil,/. 5; fruiting hypanthium and calyx,/ 6. 



Stem 4-7 dm. high, finely pubescent and with scattered long villous spreading or 

 reflexed hairs. Stipules ovate or lanceolate, 1-2 cm. long, often toothed. Basal and lower 

 stem leaves long-petioled, digitately 5-7-foliolate, glabrous or slightly silky above, silky 

 and Avhite-tomentose beneath ; leaflets obovate to oblanceolate, coarsely serrate ; stem 

 leaves sessile, 3-5-foliolate. Cyme open and branched ; flowers about 15 mm. in diame- 

 ter ; hypanthium silky-villous and finely pubescent, about 1 cm. in diameter. Bractlets 

 lanceolate, often equalling the lanceolate-triangular, more or less acuminate sepals. Pet- 

 als dark reddish purple, very broadly obcordate, exceeding the sepals. Stamens 20. 



This species much resembles P. Thurberi, from which I have recently distinguished 

 it. It differs in several characters that seem to be fairly constant, viz., the tomentum 

 on the lower surface of the leaves, the much sharper dentation, the long silky spread- 

 ing or reflexed hairs of the stem and hypanthium, and generally more acuminate sepals. 

 From the Mexican P. fusca and P. comarioides it differs in the leafiets, Avhich are serrate 

 to the very base. It seems to be more common than P. Thurberi and has about the same 



range. 



Arizona: Rothrock, No. 399, 1874; C. G. Pringle, No. 305, 1881; 1884; No. 

 1578, 1887; M. E. Jones, 1884; J. G. Lemmon, No. 2699, 1882; 1892; E. A. Mearns, 

 No. 50, 1887; T. E. Wilcox, 1893; G. C. Neally, No. 109, 1891. 



