Apr., 1923] GLEASON VERNONIA IN NORTH AMERICA I93 



the preceding species-groups. In the lack of sufficient material, the evo- 

 lution within the group can not now be discussed. 



It is not necessary to presume that only one ancestral stock of Vernonia 

 migrated into the West Indies. The seven species-groups just described, 

 constituting probably one evolutionary stock, have spread over the whole 

 region and developed into many species. Other stocks may also have 

 immigrated from South America, been isolated in certain islands, and 

 developed endemic species. Certainly two species-groups now exist whose 

 relations can not be explained, and which should probably be considered 

 as entirely distinct evolutionary lines. These are the Buxifoliae and the 

 Sagraeanae. 



The Buxifoliae include three species of the mountains of Hispaniola. 

 They are characterized by glabrous achenes, heads in. subcapitate clusters, 

 and an unusually large number of involucral scales, arranged in a beauti- 

 fully spiral imbrication. 



The Sagraeanae include ten species, nine in Cuba and one in Hispaniola, 

 with an outlying variety in Dominica, characterized by large glabrous 

 achenes and usually by large many-flowered heads. Ekman would relate 

 the group to the Bolivian V. robusta Rusby, which differs in achenes, hispid 

 in the furrows, and in the number of setae of the pappus, about 25, instead 

 of 40-70; also to the Bolivian V.obtusata Less. (V. subacuminata Hieron.) 

 which has densely hirsute achenes. There is a superficial resemblance to 

 these Bolivian plants in their heavy, rugose, reticulately veined leaves, and 

 to V. robusta also in their large heads. On the ground that specialized 

 involucral scales, few-flowered heads, and rigid, coriaceous, or tomentose 

 leaves are characters which indicate an evolutionary advance, V. Sagraeana 

 DC. and V. viminalis Gleason may be regarded as the most primitive species, 

 and V. Wrightii Sch.-Bip. and V. purpurata Gleason as the most advanced. 



We have now disposed of all leafy-bracted scorpioid species of North 

 America except two, V. yunquensis Gleason and V. segregata Gleason. These 

 Cuban species are poorly known and the former is represented in herbaria 

 only by the type specimen. While each of them exhibits certain points of 

 resemblance to other West Indian species, it is not possible to draw any 

 conclusions as to their relationships. 



The general affinities of the 57 species of the leafy-bracted groups may 

 be summarized by the diagram (fig. 1), from which it may be seen that 

 without exception the more advanced groups lie progressively farther from 

 South America, that no group is common to the West Indies and the con- 

 tinent of North America, except as introduced, and that, with very few 

 exceptions, the more advanced species of each group also lie farther away 

 from the center of origin, either in horizontal or in altitudinal distance. 



The 63 species in which the bracteal leaves are suppressed show certain 

 fundamental differences among themselves in the structure of the inflores- 

 cence, as a result of which five well-marked evolutionary stages may be 



