The Geography of Phytochemical Races

Chapter 1
Introduction
Patterns of occurrence of morphological features of a species across its natural
range can often provide insights into evolutionary relationships within the taxon.
In principal, at least, this should be no less true when the differences involve secondary
metabolites. That secondary metabolites indeed have played and continue
to play a role in systematics is borne out by the very signifi cant impact that chemotaxonomy
has had on the subject. An added feature of the use of secondary metabolites
is the extensive literature documenting the biosynthetic steps by which they
are formed, and in several cases, the genetic basis for many of the steps involved.
Thus, if the details of a given biosynthetic pathway are suffi ciently well understood,
it is often possible to infer differences in the genetic composition of species
(or populations) that differ by the presence or absence of a particular compound or
set of compounds. This application is most useful in the case of compound types
that have lent themselves to straightforward biosynthetic analysis, fl avonoids,
and simple terpene derivatives in particular. In the case of simple terpenes, where
quantitative information is more reliably available, differences in chemical structures
are less important.
Although it is possible to infer genetic differences between species, or among
populations, as mentioned above, the direction of evolutionary change in the chemistries
involved is not at all straightforward. For example, a very simple fl avonoid
profi le may be interpreted as either representing the primitive (or pleisiomorphic)
condition or an advanced (apomorphic) condition where loss of one or more members
of a pathway represents a derived condition. Only when detailed phylogenetic
analyses have been performed is it possible to say which of these positions the
profi le represents. In a few cases described below, phylogenetic analysis of the taxa
involved has been carried out, making it possible to comment on the evolutionary
signifi cance, if any, of the secondary compounds involved.
The natural product literature is vast, with only a passing comment on chemical
differences between plants from different sources occasionally included. It is
virtually impossible to track down all of these examples; thus, the examples below
represent only a sampling of chemical variation in the plant kingdom. Although not
exhaustive, the sampling does include most classes of natural products and a fairly
wide sampling of major taxa, including lichens, algae, bryophytes, ferns, fl owering
plants, and conifers.
B.A. Bohm, The Geography of Phytochemical Races,
© Springer Science+Business Media B.V. 2009
1