North American Willows 



By W. W. Rowlee 



(With Plate 9) 



1. LONGIFOLIEAE 



This group of species is clearly defined from the other sections 

 of the genus. The presence of two glands in the staminate flower 

 of most of the species and the pale deciduous scales show evident 

 affinity with the pleiandrous willows. The uniform presence of 

 two stamens led Anderson to place them with the diandrous sec- 

 tions. The same characters, however, would place some species 

 of the section Fragiles in the diandrous group. The Longifolieae 

 are evidently closely related genetically to the Fragiles. 



The long-leaved willows are confined to North America. 

 None of them are found in the arctic or subarctic regions ; two 

 occur in central and western Mexico ; the others in the United 

 States and southern Canada. The greatest number of species 

 occur in the western part of the United States, where the great 

 mountain ranges seem to limit to a considerable extent the range 

 of the different species, the consequence being that each has a de- 

 cidedly north and south range. 



Two well-marked types occur in the group, one with smooth 

 pistils, confined to the western part of the continent, the other 

 with more or less hairy pistils found across the continent. In the 

 states of the Pacific coast two distinct types may be recognized by 

 the form of the stigmas, in one 5. argophylla, etc., the stigmas are 

 short and thick ; in the other, 5. sessilifolia, etc., they are long and 

 slender. Again, the whole group diverges into two types on the 

 character of the leaves, in 6". exigaa, S. argophylla, etc., the leaves 

 are coriaceous and opaque, while in S. interior, S. sessilifolia, S. 

 melanopsis, etc., they are thin and distinctly veiny. Using th 

 together with other characters, it has been possible to make the 

 following synopsis. 



The changes in taxonomy have involved the rehabilitation of 



(247) 



