The Geography of Phytochemical Races

2.3 Europe 31
conditions revealed that pigment deposition (presumably synthesis) does not occur
if the temperature is maintained above 20°C.
2.3.4 Silene latifolia (= alba, = pratensis) (Caryophyllaceae)
This discussion features an analysis of the fl avonoid genetics of Silene latifolia and
how those data, among others, provide insights into the development of agriculture
in Europe. Before looking at the fl avonoid chemistry of the group, it is necessary
to deal with some nomenclatural matters. In the earlier literature, this taxon was
referred to as Melandrium album. Referral to Silene required the taxon to be named
S. pratensis (Rafn.) Godron and Gren., since S. alba (Miller) E. H. L. Krause had
been shown to be illegitimate by McNeill and Prentice (1981). A further change was
occasioned by the discovery of a specimen under the name S. latifolia Poiret that
carried an earlier publication date (see comments in Mastenbroek and van Brederode,
1986, p. 166). Silene latifolia is closely related to S. dioica (L.) Clairv., and
is also widely distributed in Europe. They differ in fl ower color; S. dioica has red
fl owers, whereas S. latifolia, as its earliest name recognizes, has white fl owers.
Before embarking on a discussion of Silene, a few comments on the signifi -
cance of the work are in order. Biochemical systematics or chemotaxonomy as the
subject was more often called in the 1960s and early 1970s, consisted in the early
days essentially of comparing chromatographic patterns and developing a table of
presence/absence data for the taxa under consideration. This was the “spot counting”
phase of the subject. Occasionally, statistical treatments of presence/absence
data were employed to establish levels of signifi cance of the arrays of chemical
data, which, incidentally, was an important contribution made by another fl edgling
discipline of the time, namely, numerical taxonomy. As the subject matured, more
and more attention was given to determination of exact structures and, logically,
how these structures were constructed in the cell. The establishment of biosynthetic
pathways led to the study of the enzymes responsible for individual steps
and, ultimately, to the question of the genetic control of these reactions. Flavonoids
provided particularly good test subjects for genetic studies owing to the ease of
scoring the products of controlled crosses, that is, the accumulation of intermediates
when an enzyme was absent, or, more readily, by correlating fl ower color with
genotype.
The subject more recently has progressed to the stage of probing of the genome
using allozyme/isozyme analyses, endonuclease restriction fragment analysis
(RFLP), or sequence analysis of a variety of genes themselves, although very few
of these focuses on enzymes or genes coding for fl avonoid biosynthetic reactions.
Ready availability of these techniques has tended to overshadow use of secondary
metabolites (not just fl avonoids) in systematic studies. The current situation can be
appreciated by quoting from a work by Crawford et al. (1992b) that addressed the
comparative value of the two types of data: “Flavonoid chemistry offers few advantages
over morphology because it is diffi cult, if not impossible, to infer genetic