arguments of Bernhardi (8) that Datura ceratocaula 
forms an intermediate link between the two. 
Character Differences 
The primary anatomical-morphological differences be- 
tween Brugmansia and Datura are listed in Table 1. 
Although both genera may reasonably be regarded as 
‘‘weedy’’ plants adapted to disturbed situations and to 
have shared a common ancestor or ancestors, it appears 
from an examination of their character differences that 
they have evolved as aresult of very different ecological 
pressures. 
The characters that distinguish Datura (with the ex- 
ception of Datura ceratocaula) are excellent examples 
of adaptations to a xeric environment: an annual or 
short-lived perennial life cycle, herbaceous habit, self- 
compatibility, the major part of the plant given over to 
inflorescence, and fruits that are dry, spiny, and dehis- 
cent. ‘These characters are consistent with the idea that 
Mexico and the southwestern United States is the cen- 
ter of origin and evolution of the Daturas where, during 
the ‘Tertiary, they underwent rapid adaptive radiation 
in response to developing desert environments. 
Evolving in the mesic conditions of the northern An- 
des, the Brugmansias retained several characters which 
are considered primitive relative to Datura. Among 
these characters are the bilocular ovary, self-incompati- 
bility, and the long-lived perennial condition. It seems 
likely that the Brugmansias also experienced a period of 
adaptive radiation during the late Tertiary as the Andes 
underwent their last and major orogeny, opening a 
wealth of newly disturbed habitats suitable for invasion. 
Under these conditions, they developed the arborescent 
habit, secondary woodiness, the ability to reproduce ex- 
tensively by root-suckering, pendulous flowers adapted 
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