The Geography of Phytochemical Races

2.7 North and Central America 95
Fig. 2.59 Compounds 193–198 from Helianthus maximiliani; 199–201 from Ambrosia ambrosioides;
202–205 from Ambrosia camphorata
Arizona, northwestern Mexico, and Baja California (Fig. 2.60). The species is morphologically
uniform throughout its range and is a diploid (n = 18). Earlier chemical
workers had observed some variation in sesquiterpene lactone chemistry with different
components identifi ed in material collected in Arizona and in Sinaloa, Mexico.
Seaman and Mabry collected material from 13 sites, ranging from south central
Arizona to the southern tip of Baja California, plus a site on the mainland somewhat
farther south. A defi nite difference between northern and southern populations was
observed with damsin [199] identifi ed as the major component of northern specimens
with some specimens also exhibiting damsinic acid [200]. Damsinic acid, however,
was the major component of fi ve of the six populations from southern Baja California
and the more southerly mainland population. A peculiar observation, for which no
explanation was offered, concerned two populations from mainland Mexico (numbers
42 and 43 in table). Plants from neither of these sites contained damsin or damsinic
acid, with the total lactone fraction composed of parthenolide [201]. Parthenolide was