(166) 
venient example may be mentioned V. ardorescexs and its relatives, 
all with a similar structure of inflorescence, with hirsute achenes, 
normally ovate leaves, a definite type of pubescence, and above all 
a definite and typical habit. These species-groups are in general 
characterized by a community of morphological features rather 
than by any definite and peculiar structures, and as a rule the com- 
ponent species occupy the same or adjacent territory. Ther 
good evidence that the groups in the United States include naturally 
related species of common ancestry; the presumption is that the 
groups in the tropics have the same value. But since all the spe- 
cies of Vernonia may be considered to have also a common an- 
cestry, the delimitation of large or small species-groups becomes 
merely a personal matter. 
The seven subsections of Lepidafloa by no means represent 
groups of equal value. The Scorfiotdeae reductae and Scorfiot- 
deae aggregatae are certainly derived directly from the Scorfzoz- 
deae foliatae, and are therefore subsidiary to it and not parallel 
with it. Among the Paxiculatae the dichotomae and verae are 
undoubtedly phylogenetically distinct, the latter being closely re- 
lated to the Scorpiotdeae aphyllae through a Mexican ancestry, 
while the former is endemic to Cuba and doubtless derived from 
forms similar to V. havanensis. 
Geographically the North American species may be traced back 
to an ultimate origin in South America. This is shown by the in- 
crease towards the south in number of species and in variety of 
structure and also by the fact that forms intermediate between spe- 
cies-groups invariably occur to the southward of them. Thus in 
the group Lonugifoliae, V. longifolia is most closely related to the 
more typical scorpioid forms and is distributed through the Wind- 
ward Islands. Northward, in Porto Rico and Hispaniola is the 
related V. albicaulis, while derived from or closely related to that 
species is the subsection Scorpioideae reductae of Cuba and the 
ahamas. The migration route through the Windward Islands 
into the Greater Antilles has been followed almost exclusively by 
the Scorpiotdeae foliatae. The western route through Central 
America has been followed mostly by Scorpioddeae aphyliae, and, 
further to the north by Paxiculatae. Some of the more primitive 
forms of the latter, such as the 7exazae, reach the southwestern 
United States. More specialized members of the same subsection 
have occupied the entire southeastern portion of the United States, 
