206 GENUS CHRYSOTHAMNUS. 



The members of this second major division of Chrysothamnus parryi may be assembled 

 into two apparently natural groups of three subspecies each. One of these groups con- 

 stitutes what may be called the asper line, the other the howardi line, the two differing 

 chiefly in the nature of the involucre, as indicated on the diagram (fig. 27). In the for- 

 mer subgroup, asper is given a central position, because it has undergone the least amount 

 of reduction in the number of flowers in the head. Its intermediate geographic position 

 is also to be taken into account. Farther to the west it divides into two branches. One 

 of these is vulcanicus, a subspecies of the higher Sierra Nevada, which differs in the smaller 

 average number of flowers and also in the loss of certain xerophytic features, notably the 

 stalked re.sin-glands. There is evidence, however, that the two thoroughly intergrade 

 along the east slope of the Sierra Nevada (see, for example, Congdon's numerous collec- 

 tions). The other branch has ascended even higher and culminated in subspecies jnono- 

 cephalus, which has all of the characteristics of a subalpine derivative, the stems being 

 low and divergently branched, the inflorescence reduced to one or two heads among the 

 upper leaves, and the foliage gray with a fine though sparse tomentum. It is not impos- 

 sible that monocephalus is a subalpine derivative of subspecies nevadensis, and possibly it 

 is polygenetic in origin. 



The howardi line consists of three primary and several secondary derivatives. The 

 subspecies howardi itself is a common form in the Rocky Mountains and differs from the 

 others of its line by the presence of elongated upper leaves and involucral bracts that are 

 only moderately attenuate. An unnamed modification, differing chiefly in the short 

 congested inflorescence, occurs in Wyoming. It is discussed under minor variation 18. 

 The connection between nevadensis and howardi is not direct, and possibly it passes 

 through atlenuatus; nevadensis belongs to the desert mountains and is itself polymorphous. 

 The derivation of attenuatus from howardi is more easily demonstrated, since intermediate 

 stages are represented by existing forms. Such, for example, is a form from Panguitch 

 Lake, Utah {Jones 5994, 6002z) in which the bracts are almost as slender as in attenuatus, 

 and another from South Park, Colorado, which is almost the same but with a reduced 

 number of bracts (minor variation 7). Finally, there is to be noted a possible connection 

 through attenuatus and its variation newherryi (minor variation 15) to C. nauseosus hige- 

 lovi and thence to other members of C. nauseosus. 



The accompanying diagram (fig. 27) is intended to express graphically the ideas of 

 relationships as above set forth. It is quite possible that the lines of evolution have been 

 different from those here indicated; for example, vulcanicus and its derivatives may have 

 arisen from a bolanderi-like ancestor after this was evolved from typicus. Even if this 

 could be demonstrated, it would not greatly modify the position of the subspecies as given 

 in the diagram and it is believed that those there brought near to one another are of close 

 genetic relationship, even though the direction of the evolutionary current may be in 

 doubt. 



ECOLOGY AND USES. 



Chrysothamnus parryi forms characteristic societies in climax grassland, its low stature, 

 and dense growth suggesting certain subspecies of C. viscidifiorus, as well as Gutierrezia. 

 Both typicus and howardi are frequent in the mixed prairie, the latter being found over 

 wide stretches in the foothills, on elevated plains, and in the lower mountain parks, 

 while the former occurs in the moister parks at higher altitudes. Howardi is also 

 frequently found on rocky slopes and ridges, as an open subclimax community. This 

 is in harmony with the fact that both forms are indicators of a somewhat greater 

 water-content. They occur in the original mixture of Bouteloua, Siipa, and Agropyrum, 

 but are most abundant in grama short-grass, owing to their increase under grazing. 

 They are frequently associated with Artemisia frigida, Antennaria dioeca, Chrysothamnus 



