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. acaulescens as the 
other parent. 
CoLorapo: Plains and foothills near Boulder, July, 1903, 
Tweedy 5852. 
CARDUUS ACAULESCENS X COLORADENSIS 
Carduus acaulescens (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. acaulescens 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. acaulescens 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. 
Cotorapo: Sulphur Springs, Grand Co., Aug. 8, 1907, Oster- 
hout 3615. 
CARDUUS ACAULESCENS XSCOPULORUM 
Carduus crassus Osterhout, MS. 
This was distributed under the manuscript name cited above 
and regarded by Osterhout as a distinct species. I am inclined 
