The Geography of Phytochemical Races

2.7 North and Central America 87
Fig. 2.54 Map showing collection sites for Phlox carolina study
and Arkansas (9 populations) (Fig. 2.54). Apparently, the taxon is very scarce in
Mississippi and absent from Louisiana; thus the Arkansas material represents a set
of populations disjunct from those in Georgia and Alabama.
From the 73 populations studied, no less than 71 unique fl avonoid profi les
were observed based upon two well-known fl avone hydroxylation patterns, the
apigenin type and the luteolin type, and two further compounds described simply
as “deoxygenated variants of apigenin” and called “fl avone-1” and “fl avone-2.”
Most of the compounds identifi ed were C-glycosyl derivatives of the base molecules,
nine each of the apigenin and luteolin types, the remaining four involving
fl avones-1 and -2. Structural variation arose from the nature and number
of C-bound sugars, the presence of O-glycosylated derivatives of some of the
C-glycosyl compounds, and likely the position on the parent fl avonoid where the
O-linked sugar was attached.
A casual study of this system might well have resulted in three conclusions:
(1) that variation in pigment profi les was extremely complicated (no doubt true!);
(2) that there has been comparatively little fl avonoid divergence between the two
disjunct types; and (3) that adjacent populations may or may not be more similar
to each other than they are to populations at some distance. In short, no major
geographic patterns seem to exist. However, in the hands of Levy and Fujii (1978)
this was anything but a casual study! Rather than simply presenting a matrix of
sites studied and compounds identifi ed, these authors discussed their chemical data
in terms of the minimum biosynthetic step distance (MBSD), a measure of how
closely two fl avonoids are related in terms of the number of biosynthetic steps that
separate them from their common precursor (see Levy, 1977, for the development of
this index). The authors determined that 38 biosynthetic steps are involved in arriving
at the observed fl avone array for the entire set of populations (emphasis mine).