224 GENUS CHRYSOTHAMNUS. 



RELATIONSHIPS. 



Chrysothamnus nauseosus is very distinct from all other species except C. parryi, but 

 with this it has much in common. Indeed, reduced forms of the two, in which the type 

 of inflorescence is difficult to make out, are sometimes mistaken for each other. These 

 occur most frequently in the poor soils of western Wyoming and western Colorado. 

 Often such forms can be placed with certainty only by giving close attention to neighbor- 

 ing plants in which the inflorescence may be better developed, and to any tendency 

 toward elongated herbaceous tips of the involucral bracts, this latter a mark of C. parryi. 

 A minor character, possibly indicative of the common origin of the two, is the growth of 

 long weak hairs on the tips of the corolla-lobes in certain forms. This is so unusual in 

 the Compositse that its appearance in C. parryi latior and C. pyramidatus, and also in 

 two subspecies of C. nauseosus (junceus and turbinatus) seems to have more than ordinary 

 significance. 



Variation within the aggregate here taken as C. nauseosus has been so marked that 

 numerous striking forms have resulted. The difficulty in according specific rank to these 

 has been indicated in the paragraph introductory to the key to the subspecies. The 

 problem of organizing them into natural groups is a very complicated one because of 

 the large number of characters involved and the exceptionally numerous combinations 

 of these as represented in the copious collections already made. Furthermore, it is 

 often impossible, in the absence of a detailed genetic analysis, to determine whether 

 certain forms are merely ecologic variations or whether they are based upon inheritable 

 factors. However, much time has been given to detailed field studies, to transplant 

 experiments, and to a close analysis of herbarium material. The results of these studies 

 are graphically set forth in the accompanying diagram. The statistical basis for some of 

 the conclusions is given in table 23, page 223. According to the arrangement presented in 

 the diagram, the species comprises two major assemblages of forms, three smaller groups 

 representing lines of divergence which early separated from the parent stock, and three 

 small assemblages which are believed to be marked developments from one or the other 

 of the two principal groups. Each of the units indicated in the diagram by an ultimate 

 circle is composed of one or more subspecies. Each subspecies, in turn, is usually com- 

 posed of a number of still smaller units — strains, biotypes, ecads, etc. — which are not given 

 taxonomic status, but the more noteworthy of which are discussed as minor variations. 



All of the subspecies of Chrysothamnus nauseosus are so highly specialized that it is 

 diflScult to select any one as the most primitive. However, in some cases primitive traits 

 have persisted in lines which exhibit a marked development in other features. Thus, 

 conspicuously pilose corolla-lobes, found also in C. pyramidatus and in forms of C. parryi, 

 here occur in subspecies junceus and turbinatus, occasionally also in albicaulis and bige- 

 lovi. With these and similar considerations as a clue, and recalling the close connection 

 between turbinatus and bigelovi, the opinion is ventured that the first, third, and fourth 

 primary diverging lines in the chart represent a past connection through primitive 

 forms now extinct. The second or graveolens line is in more doubt, since this may have 

 arisen directly from speciosus. Therefore, it should be understood that the placing 

 of turbinatus and its allies at the end of the taxonomic sequence does not indicate that 

 these are more highly developed than the others. 



The two larger groups of the subspecies of C. nauseosus may be referred to as the 

 typicus branch and the graveolens branch respectively. They differ from each other in a 

 number of involucral and floral characters, so that after long acquaintance with the mem- 

 bers one comes to have a fixed belief in the reality of the groups as natural units and is 

 able unhesitatingly to place a majority of the specimens he encounters in either one or 

 the other of the two assemblages. These characters, however, are so fluctuating and 

 overlapping in some of the forms that they can not be used in keys, so for this purpose 



