Rydberg : Rocky Mountain flora 551 



carduus plattensis x undulatus 



The specimen cited below was sent me by Mr. Osterhout, who 

 suggested that it was a hybrid of Carduus plattensis Rydb. and 

 C. undulatus Nutt. It has the head of the former, but somewhat 

 smaller and with narrower and less viscid bracts. The leaves 

 also are those of that species but approach those of C. undulatus. 



Colorado: Thompson's River, Larimer Co., Aug. 16, 1905, 

 Osterhout 3087. 



There are many features that suggest hybridity in Carduus 

 perplexans Rydb. In the original description, attention was 

 directed to its relationship to C. Centaureae (= C. americanus 

 Greene) and also to the C. altissimus group. At that time I was 

 inclined to regard it as a hybrid between C. americanus and C. 

 filipendulus, but the broad leaves seemed to contradict such a 

 disposition. 



Since that time I have been inclined to regard it as a hybrid 

 of C. laterifolius Osterhout and C. filipendulus, as the former 

 has broad leaves resembling those of C. perplexans. The bracts, 

 erose-tipped as they are, are not much like those of C. laterifolius. 

 Mr. Osterhout suggests that it might be a hybrid of an undescribed 

 species, specimens of which he has sent me. In these the bracts 

 resemble those of C. perplexans very much and the flowers are 

 also red; but the leaves are narrow and deeply pinnatifid. This 

 species and C. filipendulus could scarcely produce a hybrid like 

 C. perplexans. 



All the supposed hybrids given above were collected in Colo- 

 rado. Besides these the following are in the herbarium of the 

 New York Botanical Garden from neighboring states. 



Carduus megacephalus Xochrocentrus 

 There seem to be two rather distinct forms included in Carduus 

 ochrocentrus. As both are found in Texas and New Mexico and 

 I have not seen the type specimen, I am uncertain which of the 

 two is C. ochrocentrus proper. One of them extends northward to 

 Nebraska and northern Colorado and is the only one found within 

 the range of my studies. For the present I regard this as C. 

 ochrocentrus, until further information can be had. It is charac- 

 terized by strongly decurrent and strongly spinose, crisp leaves. 



