456 Rydberg : Rocky Mountain flora 



which is unknown to me, all the North American species are 

 closely related to A. Millefolium and may be only forms of that 

 species. Notwithstanding the fact that Achillea borealis, on account 

 of its large heads and numerous rays, has been placed in the 

 Ptarmica section of the genus, it is closely related to A. Millefolium, 

 and can be connected with it through two different lines of rela- 

 tionship. (See below.) It is very hard to say whether the native 

 species of the Millefolium group admitted by Pollard should be 

 regarded as species or as varieties of A. Millefolium and my inten- 

 tion here is not to express any opinion on that subject. I only wish 

 to clear certain points regarding which there seems to be a great 

 deal of confusion. I shall here use the specific names that have 

 been applied to the different forms, whenever such are available. 



Achillea Millefolium L. Sp. PI. 899. 1753 

 This is a native of northern Europe and I think also of northern 

 New York and New England and eastern Canada ; at least it has 

 naturalized itself in that part of North America. Elsewhere it is 

 only sparingly introduced. It is a characteristic northern plant. 

 It differs from all the other native forms in being less villous and 

 having shorter hairs. The rachis of the leaves is distinctly wing- 

 margined and the primary segments more or less decurrent; they are 

 usually decidedly spreading. The secondary segments are short, 

 lanceolate, and spinulose-tipped. The rays are comparatively 

 large, 2-3.5 mm - broad. The bracts have usually brown margins. 

 In the far north, the plant often becomes more hairy and the 

 margins almost black, and it approaches A. borealis on one hand 

 and A. lanulosa on the other. Of such specimens we have one 

 from North Iceland, collected by Olasur Davidson, and two col- 

 lected by Collins and Fernald, one at Carleton Point, Que., in 

 1904 (labeled A. lanulosa) and the other at Mt. Albert, Que., in 

 1906, no. 25 j (labeled A. borealis). 



Achillea occidentalis Raf.; DC. Prod. 6: 24. 1837, 

 as a synonym under 



A. Millefolium occidentalis DC. loc. cit. 



A. Millefolium Pollard, Bull. Torrey Club 26: 371, in part. 1899. 



Not A. Millefolium L. 1753. 



This is evidently the plant that Pollard took for the real 



