Apr., 1923] 
GLEASON — VERNONIA IN NORTH AMERICA 
193 
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. (F. 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 F. 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 
