The Geography of Phytochemical Races

94 2 Examples Within Continents
that the two populations clearly belong to the same species. Additional weight to
the argument came from observations that Flyriella parryi (A. Gray) R. M. King &
H. Robinson, a segregate from Brickellia generally accepted by systematists, presents
a fl avonoid profi le based upon quercetin, quite unlike the profi les that characterize
Brickellia. Outgroup situations of this sort are not commonly encountered in
systematic applications of secondary metabolites; their value is highly signifi cant.
The studies of variation patterns in Lasthenia and Brickellia hardly break the
surface of a vast and complex literature on chemical variation within Asteraceae.
The subject has been discussed in detail, with reviews focusing on polyacetylenes
(Bohlmann et al., 1973), sesquiterpene derivatives (Seaman, 1982), and fl avonoids
(Bohm and Stuessy, 2001). The next examples come from the sesquiterpene lactone
literature and, again, represent only a sample of the applications that have
been made using those data. Examples covering the taxonomic hierarchy within
Asteraceae up to the early 1980s can be found in the monumental review of the
family prepared by Seaman (1982).
2.7.7 Helianthus maximiliani (Asteraceae)
The fi rst example involves the sesquiterpene lactones from Helianthus maximiliani
Schrader initially described by Herz and Kumar (1981). Working with plant material
collected in Coffey County, Kansas (see Fig. 2.57), those workers isolated and identifi
ed several closely related heliangolides exemplifi ed by compounds [193, with a
second set having a double bond at the starred position] and [194] (see Fig. 2.59
for structures 193–205). Subsequently, Gershenzon and Mabry (1984) examined
a population of this species from Travis County in south-central Texas. The chemistry
reported by these latter workers was completely different from the array of
compounds obtained from the Kansas collection consisting of fi ve guaianolides,
represented by [195], where the R group represents a series of aliphatic acids, the
germacranolides [196 and 197], and the labdane derivative [198]. A further collection
of this species from a north central Texas population showed an array of compounds
consisting of [197] and its (2′S,3′R)-epoxyangelate isomer, but no heliangolides or
guaianolides. This infraspecifi c lactone variation was not considered unusual by
those workers who pointed out that chemical races have been reported in Ambrosia,
Artemisia, and Iva, among other genera, referring to Seaman’s (1982) review.
2.7.8 Ambrosia (Asteraceae)
The next examples concern species of Ambrosia L. that are characterized, in the fi rst,
by a north–south variation, and in the second, an east–west one, with the added feature
of different ploidy levels. The work is that of Seaman and Mabry (1979a, b). In the
fi rst example, we will look at A. ambrosioides (Cav.) Payne sampled from southern