﻿SHERFF—BIDENS 



Pittonia 4:254. 1901; Bidens lugens Greene, loc. cit.; Bidens formosa 

 Greene, loc. cit. 264; Bidens Parryi Greene, loc. cit. 265; Bidens 

 persicae- folia Greene, loc. cit. 266. 



The types of Bidens chrysanthemoidcs Michx. and B. helianthoides 

 H.B.K. (both in Herb. Mus. Hist. Nat. Paris) appear precisely the 

 same. The original description of both species shows their achenes 

 to have been 2-aristate in each case, although many specimens have 

 since been gathered showing the achenes often 3 or 4-aristate. A 

 study of numerous specimens from the United States and Mexico 

 seems to indicate a slight tendency for the western specimens to be 

 more often 2-aristate, the eastern ones more often 3 or 4-aristate. 

 But the variations are so abundant as to defy all attempts at 

 delimiting the separate forms or races in a specific way (cf. Torr. 

 and Gr. FL N. Amer. 2:353. 1842). 



Greene cites a single sheet for B. formosa, a plant from Dela- 

 ware County, Pennsylvania. But in the Field" Museum are 5 

 sheets of material (all by /. K. Small, Wetzel's Swamp, N. Harris- 

 burg, September 1887) from the same state, and these show all 

 gradations between B. formosa and B. laevis. Again, Greene 

 terms his B. Parryi an unwelcome species, "as uniting the habit 

 of B. cernua and the fruit of the Platycarpaea group of species." 

 But even if B. Parryi were a valid species, it would not be the first 

 species to do this; for all the material of B. laevis that has flat, 

 biaristate achenes does the same; and, moreover, B. radiata Thuill. 

 (B. platycephala Oerst.) had long been noted as a species that 

 likewise united B. cernua with B. tripartita, the latter a principal 

 species of the Platycarpaea group (cf. G. Schweinfurth, Yerhand. 

 Bot. Verein Prov. Brand. 2:145. 1861). Indeed, Greene himself, 

 on another occasion {loc. cit. 261) had been led to consider B. radiata 

 in this same connection, having suspected his B. leptopoda as being 

 this species. DeCandolle, in monographing the genus Bidens 

 (Prodr. 5:594. 1836), defined the subgeneric section Platycarpaea 

 with the evident purpose of admitting just such species as 

 B. cernua, and actually classed B. cernua among the Platycarpaea. 



specks was very keenfthere is no questior^as to hfe accuracy. LinnaeiJ private 

 i'":->55- . '.m. Pi rsoon, Synops. Plant. 2:473. 18071. 



