UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



BOTANY 



Vol. 7, No. 6, pp. 159-181 . November 7, 1919 



o~> 



I. CHRYSOTHAMNUS NAUSEOSUS AND ITS 



VARIETIES 



HARVEY MONROE HALL ,'2 . 

 QAHDEN 



CONTENTS 



PAGE 



I. Tntioduction and acknowledgments 159 



IL Key to the varieties of Chrysothamnus nauseosun 163 



III. Synopsis of the varieties of Chrysothamnus nauseosus 165 



IV. Index of specific and varietal names 181 



I. INTRODUCTION AND ACKNOWLEDGMENTS 



In the course of an investigation of Chrysothamnus as a possible 

 source of rubber, it has been found necessary to give considerable 

 attention to the botanical relationships of the species and varieties of 

 this genus of shrubs. Even before that investigation was begun in 

 1917, the author had undertaken a revision of the group and although 

 the preparation of this has been delayed by the rubber studies it is 

 intended now to carry it forward to completion. In the meantime, 

 however, it is necessary that the forms discussed in the rubber report 

 be properly defined and that those not hitherto recognized be named 

 and described. These are the rea.sons for tlie publication of this 

 preliminary paper. 



Chrysothamnns is a genus of the Aster Tribe of the Compositae 

 and belongs to what is often called the Haplopappus group. From 

 related genera it differs chiefly in the more cylindraceous involucre, 

 the bracts of which are usually more or less keeled and tend to fall 

 into five vertical ranks. Although these characters are too variable 

 to give to the genus that sharpness of delimitation that one would like, 

 yet there can be no question as to its homogeneity. It represents what 



