548 RYDBERG: Rocky MOUNTAIN FLORA 
to think it a hybrid of the two species mentioned for the following 
reasons. The form and the pubescence of the leaves are almost 
exactly those of Carduus acaulescens. The small and clustered 
heads also suggest that species; but the plant has an evident stem 
and the involucre is decidedly arachnoid-hairy. As C. scopu- 
lorum and C. Parryi are the only species in Colorado which have 
arachnoid involucres, one of these may be supposed to be the other 
parent. As C. Parryi has also dilated erose bracts, it must be 
thrown out of consideration. In C. crassus the involucral bracts 
have also the long slender spines characteristic of C. scopulorum. 
CoLorapo: Sulphur Springs, Grand Co., July 17, 1905, Oster- 
hout 3042. 
Neither of the two supposed parents is represented by speci- 
mens from Sulphur Springs, but there is a specimen, Osterhout 
3615, just cited above, which I regard as a hybrid of C. acaulescens 
with another species. 
CARDUUS GRISEUS XLATERIFOLIUS 
Carduus canalensis Osterhout, MS. 
This I included in Carduus griseus in my Flora of Colorado 
but it differs in many respects from the type of that species, the 
leaves being much broader and less lobed, the upper leaves with 
broad auricles and the inner bracts with dilated erose tips. These 
two characters suggest C. laterifolius, from which it diffets in the 
long and broad spines of the outer bracts, characteristic of C. 
erosus. 
CoLorRADO: Canyon of Thompson River, Larimer County, 
August 16, 1905, Osterhout 3080. 
This specimen was collected together with the type number of 
C. laterifolius, viz., Osterhout 3090 (the next number). 
CARDUUS GRISEUS X SCOPULORUM 
Carduus Osterhoutii Rydb. Bull. Torrey Club 32: 131. 1905. 
This has the habit, the leaf form, and the long flat spines of the 
bracts of Carduus griseus, but the inflorescence is conspicuously 
arachnoid-hairy as in C. scopulorum and the leaf segments are 
rather more numerous than in C. griseus. The following speci- 
mens belong here: 
