Rydberg : Rocky Mountain flora 547 



at the tip, the leaves have more lanceolate lobes and stronger 

 spines, and the stem and midribs of the leaves are more or less 

 arachnoid-hairy. The clustered heads, the arachnoid pubes- 

 cence on the stem, and almost glabrous bracts, with broad bases 

 gradually tapering upwards, would suggest C. acaidescens as the 

 other parent. 



Colorado: Plains and foothills near Boulder, July, 1903, 

 Tweedy 5852. 



Carduus acaulescensXcoloradensis 



Carduus acaidescens (A. Gray) Rydb. and C. coloradensis 

 Rydb. are closely allied and many regard them as forms of the 

 same species. As they often grow together and intermediate 

 forms are found, this disposition seems plausible, but these inter- 

 mediate forms may as well be explained by hybridity. The typical 

 C. acaidescens has practically no stem and the small campanulate 

 heads, seldom more than 3 cm. wide, are sessile and congregated 

 in a flat-topped head-like cluster, while the typical C. coloradensis 

 has a stem 3-10 dm. high and the larger heads are more or less 

 peduncled, 4-7 cm. broad, hemispheric, and scattered. The 

 intermediate forms are usually low-stemmed and the heads, inter- 

 mediate in size and shape, are in a dense flat-topped cluster at 

 the end of the stem. At the south end of Fish Lake, Utah., 

 C. acaidescens and C. coloradensis were found together by myself 

 and Mr. Carlton and the specimens in the New York Botanical 

 Garden bear the numbers 7547 and 7546, respectively. The 

 supposed hybrid also was collected, although I can not find any 

 specimens now in the collection of the New York Botanical 

 Garden. They may have met the same fate as some other speci- 

 mens of the collection in being damaged by rain. There is one 

 specimen, however, in our herbarium, which I regard as belong- 

 ing to this hybrid, viz. 



Colorado: Sulphur Springs, Grand Co., Aug. 8, 1907, Oster- 

 hout 3615. 



Carduus acaulescens X scopulorum 



Carduus crassus Osterhout, MS. 



This was distributed under the manuscript name cited above 

 and regarded by Osterhout as a distinct species. I am inclined 



