The Geography of Phytochemical Races

2.3 Europe 43
Table 2.7 Essential-oil composition of Cistus monospeliensis from different substrates (from
Robles and Garzino, 2000)
Compound Substrate
Calcareous Siliceous
α-Cadinol 3.17 ± 1.43a Not detected
Unknown (peak N) 37.62 ± 16.58 15.16 ± 9.79
α-Bisabolol 34.96 ± 32.49 1.60 ± 0.67
Unknown (peak R) 12.54 ± 6.81 30.70 ± 14.10
Diterpene (peak T) 45.03 ± 19.26 84.75 ± 40.50
a Concentration expressed in µg/µl sample injected (GLC).
Additional information on essential oil variation in C. monspeliensis comes from
a study by Angelopoulou et al. (2002) who were interested in diurnal and seasonal
patterns. Signifi cant differences were noted during both time periods. It would be
of interest to learn what effects cultivation in a common garden environment would
have on oil expression in these species.
A second study featuring Cistus involves an analysis of the essential oils of
plants collected from nine sites on the island of Crete, three from the western
end of the island and six from the eastern end (Angelopoulou et al., 2001). In the
study, 114 compounds were identifi ed, although many of them were present in
very small amounts and only in some populations. Few compounds could be
described as dominant with the possible exception of carvacrol [89] (see Fig. 2.24
for structures 89–91), which was present at the level of 20.23% in one of the
eastern populations, 11.13% in another, and was absent from only one of the nine
populations. Caryophyllene oxide [90] reached 11.24% in one population and
had one of the more consistent ranges, with the lowest percentage being 2.86%.
Other compounds of note are dehydroabietol [91], which reached 10.01% in one
population, and hexadecanoic acid (C-16 acid; 16:0) whose contributions ranged
from 4.24% to 20.63% with the highest concentrations recorded for two of the
western populations. Numerical analyses of the total data set revealed considerable
structure in the data set with clear-cut distinction between an eastern and
western chemotypes. Those authors failed to fi nd any variation in morphological
features throughout the range of this taxon on Crete. Comparisons with other species
of Cistus in Greece—numbering seven—is not possible owing to the lack of
comparable studies on the other taxa.
While referring to the island of Crete, it is convenient to look briefl y at a recent
study of monoterpenoid diversity of Origanum microphyllum (Lamiaceae) on the
island. Extremes in monoterpene composition ranged from specimens rich in sabinene
[92] (see Fig. 2.24) and its trans-hydrate derivative to specimens rich in cissabinene
hydrate (Gotsiou et al., 2002). No geographic patterning was observed
among the populations whose chemistries were not altered by growth in common
garden experiments. The paper by those workers offers excellent leading references
to patterns of variation in other members of Lamiaceae.