The Geography of Phytochemical Races

296 7 Polar Disjunctions
occurs throughout much of the range of the genus. Specimens of this taxon from
Peru, Sonora, Mexico, Baja California, Mexico, and southern California were analyzed
for their fl avonoid aglycones by Crins et al. (1988b), who identifi ed a series
of O-methylated fl avonols and fl avanones. The simplest compounds identifi ed were
kaempferol 3-mono- and 3,4′-dimethyl ethers; all others possessed 6-O-methoxylation.
The sole fl avanone isolated was identifi ed as eriodictyol 7-methyl ether.
The authors of the survey attempted to infer phylogenetic relationships using
several parsimony criteria. Although a reasonably parsimonious set of relationships
among the members of the subtribe (the study included Amauria, Pericome, and
three sections of Perityle) emerged from the treatment, serious problems surround
this type of analysis, however, insofar as only a single set of data was involved.
Adding to the problem is the possibility of highly reticulate biosynthetic pathways:
the 6-oxygenation and O-methylation profi les can be arrived at by various combinations
of the two processes. The authors pointed out that there is an increase in
the complexity of the fl avonoid profi le of P. emoryi as one goes northward in its
range. This trend has been noted in other taxa: Arnica (Wolf and Denford, 1983),
Chenopodium (Crawford and Mabry, 1978), Chrysosplenium (Bohm and Collins,
1979), and Phlox (Levy, 1983). A fi nal comment on this species’ lifestyle might also
be signifi cant. Perityle emoryi is a self-compatible, polyploid (hexaploid and octaploid)
(see Powell, 1974) that may have undergone fi xation of local races, chemical
in the present context, as it spread throughout the western parts of North America,
Mexico, and parts of South America.
7.10 Tradescantia (Commelinaceae)
Tradescantia, a genus of perhaps 70 species (Mabberley, 1997, p. 720), occurs
exclusively in the New World, but therein enjoys an interesting disjunct distribution.
For the purpose of the present discussion we can follow Del Pero Martinez and
Martinez (1993) in their description of three major areas of occurrence: (1) North
America to the Mexican border; (2) Texas, New Mexico, and Mexico (excluding
Baja California and much of northwestern Sonora) to the border with Guatemala;
and (3) South America. Those workers examined 90 individuals representing 42
species from the entire range of the genus. A rich array of phenolic compounds
was reported based upon C-glycosyl derivatives of apigenin and luteolin, fl avone
O-glycosides based upon luteolin, tricin (5,7,4′-trihydroxy-3′,5′-dimethoxyfl avone)
[608], and 6- and 8-hydroxyluteolin [609 and 610, respectively] (see Fig. 7.5 for
structures 608–610), O-glycosides of kaempferol, quercetin, and isorhamnetin, and
hydroxycinnamoyl glucose ester sulfates.
Three distinct chemotypes were observed. Taxa from each of the three areas
noted above exhibited unique combinations of the compounds and compound
types, although there was a degree of variation within most groups, as one might
expect. The North American chemotype was characterized by very high frequency
of the sulfated cinnamic-acid derivatives, a frequency of fl avonol derivatives of