The Geography of Phytochemical Races

5.1 Vascular Plants 219
in the graphing of values seen in Fig. 5.1. The correlation of evolutionary advancement
values, without reference to individual taxa, indicates that the European taxa
have substitution patterns most closely resembling the base structures, the Australian
specimens are a little more complex (advanced, specialized?), and the Asian and
North American taxa display highly derived B- and A-rings, respectively. This in turn
suggests that the xanthone containing Gentianaceae originated in temperate Europe,
and their spread into new areas was accompanied by structural changes associated
with one ring or the other.
Other examples in the Gottlieb and Kubitzki (1983) paper, following similar
statistical methodology and logic, concern chemical changes in the evolution of
Aniba (Lauraceae) in the Amazon, and associated river basins; and relationships
among genera of Papilionoideae as a function of their accumulated alkaloids. These
are complex examples that would repay careful study by interested readers.
5.1.3 Hordeum (Poaceae)
Hordeum vulgare L. and several closely related species have been important elements
in agriculture for a very long time. Mabberley (1997, p. 346) informs us that barley
was fi rst harvested some 11,000 years ago. In the 1960s, Fröst and his colleagues
undertook studies of the fl avonoids of barley and its relatives as a possible source of
information in tracking routes of movement of this valuable food plant (Fröst and
Asker, 1973, 1977; Fröst and Holm, 1971, 1972, 1977; Fröst et al., 1975, 1977). The
early survey studies revealed the existence of three clear-cut chemical races—called
A, B, and C—based upon their fl avonoid spot profi les. Analysis of 1424 local varieties
was made, along with samples of H. spontaneum and H. agriocrithon (Fröst and
Holm, 1975). Chemotypes A and B (there was further differentiation of type B into
two subforms but this fact does not infl uence the overall picture) were observed in
varieties from throughout much of the world, including collections made in Europe,
Asia, the Middle East, Africa, and North America. Race C, on the other hand, was
observed primarily in varieties collected in Ethiopia (238 of 279 varieties tested).
These workers surmised that race C had evolved from race B, followed by selection.
Structural studies of the fl avonoids revealed the profi les to consist of O- and
C-glycosyl derivatives of the common fl avones, apigenin, luteolin, and chrysoeriol.
The bulk of the variation observed results from the nature of the sugar attached to the
6-C-glucosyl fl avones (Fröst et al., 1977).
5.1.4 Pteridium aquilinum sens. lat. (Pteridaceae)
The toxic properties of Pteridium aquilinum L., the common bracken fern, have
been known to humankind for a very long time. Two principal causes of trouble are
its carcinogenic properties (M. Saito et al., 1975; I. A. Evans, 1976; Hirono, 1986)