The Geography of Phytochemical Races

56 2 Examples Within Continents
well-known species, most of which are of commercial importance. The literature
dealing with chemical constituents of aromatic plants of the Mediterranean region
and the Middle East is extensive. The examples below are only a sampling, but
clearly show the existence of signifi cant differences among populations, and species,
of many plants.
Pistacia lentiscus L. (Anacardiaceae) (mastic; dessert and confectionary seeds,
pistachio, come from P. vera L.) grows widely in countries bordering the Mediterranean
Sea. In addition to its natural range, the species is much cultivated in Corsica.
Castola et al. (2000) analyzed the essential oil from leaves of 105 individual plants,
representing much of the natural range on the island. Three main chemotypes were
identifi ed, with one of them further divisible into two subgroups: (1a) α-pinene
(22) and terpinen-4-ol [42] with terpinen-4-ol predominating; (1b) α-pinene and
terpinen-4-ol with α-pinene predominating; (2) limonene [24] plus terpinen-4-ol
type; and (3) myrcene [40]. No correlation between geographic region and essential
oil composition was found in this study (Cassanova, personal communication).
Geographical differences do exist, however, within this species. Studies from
other parts of the Mediterranean Basin had shown that Pistacia from Sardinia (Picci
et al., 1987) and southern France (Buil et al., 1975) had profi les similar to Corsican
types 1a and 1b, respectively. Spanish and Sicilian oils had much lower myrcene
concentrations than seen in Corsican type 3 (Calabro and Curro, 1974; Boelens and
Jimenez, 1991). Leaf oil from Moroccan plants had α-pinene, myrcene, limonene,
β-caryophyllene, and a cadinene isomer in roughly equivalent amounts (Guenet
and Aubanel, 1991). Oil from plants growing in Egypt was unique in accumulating
large amounts of 3-carene (δ-carene) (DePooter et al., 1991). Differences in fruit
oils from different geographic origins were also noted: Spanish material gave values
for myrcene, α-pinene, and limonene of 72%, 10%, and 7%, respectively (Boelens
and Jimenez, 1991), while the same compounds in Australian material were present
to the levels of 39%, 28%, and 11% (Wylie et al., 1990).
From the data available, it is diffi cult to explain the apparent plasticity of volatile
compounds produced by plants from these different areas. Subtle environmental
factors may be at work. Alternatively, selection for oil yield, particular oil composition,
or for some other feature, over the years may have resulted in the variation
now seen. The variation seen in Corsican plants may have arisen through the arrival
on the island of propagules originating in the other growing areas. In areas so long
occupied by humankind, it is often diffi cult to sort out purely natural driving forces
from the effects of cultivation.
2.4.5 Thymus (Lamiaceae)
Studies of the essential oils of Thymus species have documented the existence of several
chemotypes with greater or lesser geographical distinctions among them. In an
examination of the essential oils of T. vulgaris L. native to France, Granger and Passet
(1973) described six chemical phenotypes based upon the occurrence of a number