546 Rydberg : Rocky Mountain flora 



Carduus americanusXspathulatus 

 This resembles most C. americanus in habit and leaf-form; the 

 bracts are somewhat erose on the margins as in that species, but 

 they are scarcely at all dilated, and if so only the innermost, and 

 they are tipped with the short and broad spines characteristic of 

 C. spathtdakis. To this are referred: 



Colorado: Estes Park, Aug. i6, 1905, Osterhout jogi; Sulphur 

 Springs, July 16, 1905, Osterhoiit 3057; Happy Hollow, July 14, 

 1898 (collector not given). Herb. State Agric. College, no. 2801. 

 The last was distributed as Carduus griseus and has perhaps 

 given rise to a wrong impression of that species. C. spathiilatns 

 was then undescribed and the bracts excluded no. 2801 from C. 

 americanus. We have no specimens of either of the supposed 

 parents, from exactly the same locality, but C. americanus is found 

 nearly everywhere in the mountains of northern Colorado, and 

 Osterhout in the original description of C. spathulatus states that 

 it is common on both sides of the range of mountains east of the 

 North Park. 



Carduus americanus X coloradensis 

 Carduus erosus Rydb. Bull. Torrey Club 28: 507, 1901. 



This was originally described as a distinct species. Professor 

 Nelson reduces it to a synonym of Carduus americanus. The 

 broad hemispheric head, the broad bracts with less dilated tips, 

 and the more spiny leaves with more numerous and lanceolate 

 lobes are very different from those of the typical C. americanus. 

 The form and structure of the involucre, the form of the leaves, 

 and the habit approach those of C. coloradensis. The upper 

 surface of the leaves and the midrib beneath show some of the 

 arachnoid hairs characteristic of C. coloradensis and its allies. 

 We have no specimens of the two supposed parents from Durango, 

 the type locality of C. erosus, but the locality is not without the 

 range of either. 



Colorado: Durango, 1896, F. Tweedy 517. 



Carduus acaulescensX americanus 

 This resembles most C. americanus, but the stem is lower, 

 the heads crowded, the involucral bracts elongated and less dilated 



