The Geography of Phytochemical Races

2.4 The Mediterranean Basin 57
Fig. 2.35 Compounds
125–130, terpenes from
Thymus species
of common monoterpene derivatives, namely, geraniol, linaloöl, carvacrol, and thymol.
Although population differences were minimal, there was some differentiation,
particularly with regard to populations rich in thujanol-4 [125], which tended to lay
roughly west of Marseilles (see Fig. 2.35 for structures 125–130). Cañigueral et al.
(1994) studied T. moroderi Pau ex Martinez and T. antoninae Rouy & Coincy collected
in Spain. These workers found little chemical polymorphism in T. antoninae,
but clear-cut differences in the sesquiterpene components of T. moroderi were evident.
Thus, plants from near Alicante (38°21′N, 0°29′W) were distinguished on the
basis of sesquiterpene composition from those collected around Murcia (37°59′N,
1°8′W). Plants from both areas had very similar monoterpene profi les. Sáez (1999)
reported wide chemical variation, with no apparent geographical races in another
Spanish species, T. baeticus Boiss ex Lacaita. Studies of a third Spanish species,
T. piperella L. revealed a degree of geographic patterning with regard to one of three
chemotypes (Blanquer et al., 1998) involving p-cymene [126], γ-terpinene [127],
carvacrol [89], and thymol [105]. The three chemotypes defi ned were: (1) p-cymenecarvacrol-γ-terpinene
(11 populations); (2) p-cymene-thymol (5 populations); and
(3) p-cymene-carvacrol (15 populations). The distribution of chemotypes 1 and 3 can
best be described as showing tendencies rather than clear-cut differences: chemotype
1 was found most often in northern populations (west of Valencia), while chemotype
3 was found most often in the southern part of the study range (north of Alicante).
Chemotype 2 was observed in fi ve populations clustered more or less in the center of
the study range (about half way between Alicante and Valencia).
The fi nding of Mártonfi et al. (1994) that chemotype patterns in T. pulegioides
L. depend to a signifi cant degree upon soil chemistry may prove of wider signifi cance
in trying to establish the driving forces behind the level of variation seen in oil composition.
Although many of the studies of variation involve plants that are of some commercial
importance, with variation playing a signifi cant part in quality of the product,
purely biological considerations are also interesting. For example, Beker et al. (1989)
studied the volatile components of two chemotypes of Marjorana syriaca L. as to
the effect that the different chemistries (thymol/carvacrol ratio) had on honeybees.
These studies indicated that bees can discriminate among the four “odor identities:”