The Geography of Phytochemical Races

Abstract
The discovery of chemical races was one of the important outcomes of the “chemotaxonomic
age,” providing systematists with another tool in the search for relationships.
The subject was discussed in a few review articles at the time, but, by and
large, receded into the background as more powerful techniques, generally referred
to as molecular biology, came on stream. This review is an attempt to update the
subject of chemical races by bringing together an assortment of examples from
the literature where geographically distinct profi les in the occurrence of secondary
metabolites have been described.
The examples are sorted into several general categories, within which examples
are further arranged according to geographical areas. The fi rst major category
involves disjunctions that occur more or less within continents, with some obvious
exceptions such as some African taxa that not only occur primarily on the continent
but are also represented on Madagascar or on the Canary Islands. The second category
is similar to the fi rst, but specifi cally addresses distributions likely caused by
retreat of glaciers. The third category treats intercontinental disjunctions; category
four is similar, but treats examples characterized by wide disjunctions that do not fi t
easily into the intercontinental group. Category four also includes several examples
from the lichen chemistry literature. Category fi ve features disjunctions involving
oceanic islands, while polar disjunctions are covered in the fi nal section.
Inclusion of an example in a particular category is admittedly arbitrary. Examples
in the postglacial group, for instance, could just as easily have been included
within the continental group, but were given special consideration because most of
the workers involved with those taxa discussed their results in terms of refugia and
postglacial migration. Some taxa appear under two or more categories. For example,
some taxa within Chrysosplenium are disjunct between Asia and North America,
others between North America and Europe, and still others between Asia and South
America. At closer focus, one fi nds sectional disjunctions between eastern and
western North America, and in one case, populational differences within a species.
Unfortunately, few systems have been examined this thoroughly, as will be noted in
several places below.
In a few cases, information obtained from macromolecular methods is included
where such data might have a bearing on interpretation of how a given secondary
metabolic profi le could have come about. Specifi cally, it is possible to speculate on
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