The Geography of Phytochemical Races

4.1 Across the Atlantic Ocean 179
Fig. 4.4 Map showing the spread of Cakile in Australia, north to approximately 30°S and east to the
coast of Victoria. The northward spread was likely halted by increasing ocean water temperature
Some years ago, Breckon and Barbour (1974) published a review of beach vegetation
for the North American Pacifi c Coast that contains detailed information on a
wide variety of strand taxa. A number of taxa discussed in their work have disjunct
distributions, involving other continental beaches suggesting other taxa worthy of
detailed phytogeographic study.
4.1.4 Cypripedium calceolus (Orchidaceae)
In this example, we examine differences in the fl oral aroma chemistry of three
“species” of Cypripedium as determined by Bergström et al. (1992). Before the
recognition of the North American species (C. parvifl orum with two or three varieties),
C. calceolus L. was thought to consist of three entities, whether varieties or
subspecies is not relevant, the European “calceolus,” and two North American entities,
“parvifl orum” and “pubescens.”
A key factor for survival of these organisms is that they must resort to a chemical
strategy to overcome the absence of nectaries in their efforts to attract pollinators.
It has been observed that the most important structure for attracting bees
to these fl owers is the staminode, which appears to be the source of the volatile
attractants. Using plants maintained in a common garden, Bergström et al. (1992)
analyzed the fl oral-fragrance components of the three entities, selected results of
which are summarized in Table 4.2. The table includes the information in two
forms, concentrations of individual components in the upper panel with a notation