RELATIONSHIPS AND GENERIC LIMITS. 33 



Phil. Soc. II. 7:417, 1841) and reduced to Artemisia, section Dracunculus, by D. C. 

 Eaton (Watson, Bot. King's Expl. 180, 1871), which reduction was accepted by Bentham 

 and Hooker, Gray, Hoffmann (in Engler and Prantl's Natiirlichenpflanzenfamilien), 

 and by others. Recently it has been revived by Rydberg and others, but without addi- 

 tional substantiating characters. Its most striking feature is the villous pubescence of 

 the achenes and corollas. This can not be considered of generic or even of sectional 

 value, since, aside from the fact that such characters are never of prime importance, 

 the recognition of Picrothamnus would lead to claims for generic rank for such species 

 as A. parishi, in which the achenes are arachnoid-pubescent, while the corollas remain 

 glabrous, and which is also of such close natural relationship to Artemisia tridentata 

 that it is here taken as a subspecies. The spinescent habit is not exactly dupUcated 

 elsewhere in the genus, but it is approached in A. rigida and in some forms of the Asiatic 

 A. persica Besser, one of which, described as variety subspinescens (Besser, Fl. Orient. 

 3:374, 1873), has similarly rigid branches that are persistent and indurated after anthesis. 

 This does not belong to the same section as spinescens, but its tendency to become 

 subspinose indicates that the habit need not exclude a form from the genus. Another 

 feature of spinescens is found in the completely fused style-branches. Since this fre- 

 quently occurs also in several species of the section Dracunculus, as discussed under 

 the heading of Criteria, it seems to be an additional bond between Picrothamnus and 

 Artemisia, especially when the high evolutionary position of Dracunculus is considered. 

 Any other arrangement would necessitate the assumption that the fused character of 

 the style-branches was developed independently in two widely separated groups. 



Finally, Artemisiastrum , which has been proposed as a new genus to include A. palmeri 

 alone, is an evident recognition of the importance of receptacular bracts. While the 

 presence or absence of these structures is of much value in the classification of the 

 Compositae, their occasional occurrence in a genus whose species are almost universally 

 devoid of them may be looked upon as a possible case of reversion rather than as the 

 basis for a new genus. In fact, it is not uncommon for certain of the Helenieae to exhibit 

 chaff on the receptacle of species in which it is usually naked, yet there is no thought 

 of separating these aberrant forms even as species (Baeria chrysostoma, Chaenactis 

 carphoclinia, etc.). Since the other characters of Artemisiastrum are not fundamentally 

 different from those of other species of the section Seriphidium, the presence of recep- 

 tacular chaff may be considered of not more than specific value in this case. An attempt 

 to assign the same value to a character wherever it appears, for the sake of consistency 

 or otherwise, would lead to the creation even of new tribes for A. palmeri and for the 

 occasional forms of Baeria and Chaenactis just mentioned, on the plea that this character 

 is used elsewhere in the Compositae for the differentiation of tribes. 



From the considerations just presented it seems impossible that Picrothamnus and 

 Artemisiastrum are other than offshoots from the main line of Artemisia, and further- 

 more that each has arisen at a different point. There is no evidence to indicate that 

 either was developed before the differentiation of other Artemisias took place; in other 

 words, that they represent phylogenetic lines distinct from Artemisia. Their defense 

 must rest, therefore, upon the plea that their differentiating characters are such as are 

 used elsewhere for generic distinction, but such treatment leads neither to stability nor 

 to an expression of the facts of evolution and relationship as they are now understood. 

 For these reasons, these proposed segregates are here again referred to Artemisia. 

 Crossostephium is an entirely different case. When restricted to its single original species 

 it represents a definite phylogenetic hne distinct from Artemisia. After the ehmination 

 of the American species, recently referred to it, but which belong to Artemisia, Cros- 

 sostephium has good characters as a natural monotypic genus. 



