The Geography of Phytochemical Races

36 2 Examples Within Continents
Mastenbroek (1983) posed two questions: (1) Did S. latifolia follow the spread
of agriculture in Europe? (2) What was the impact of glaciation on the history of
S. latifolia? Because S. latifolia requires open ground for successful colonization,
it could not have advanced into central and northern Europe until appropriate
habitats became available. This was accomplished through the deforestation that
accompanied preparation of the land for planting. Mastenbroek (1983) suggested
that S. latifolia existed in its natural state in nonarable sites in southern Europe
and the Middle East at the time that human migration northward began. With the
availability of newly cleared sites, establishment of weedy forms likely occurred.
These could then have spread by different routes, northward and northwestward
from the Balkans, and westward toward the Iberian Peninsula. Differentiation into
proto-western and proto-eastern forms (races) may have occurred at that time.
Owing to diffi culties in identifying seeds and pollen as coming specifi cally from
S. latifolia, it is impossible to state with certainty that the species per se was the
progenitor of the modern races, or whether it evolved from some other species
near the time of expansion. At any rate, expansion of the weedy forms continued
as more and more sites became available leading to eventual contacts from which
the present-day intermediate forms arose.
In addressing the issue of postglacial history of S. latifolia (or its progenitor),
it is necessary to consider where it existed during the time when ice covered most
of northern Europe. The species is not well adapted to survive in cold conditions
(Thompson, 1973), which Mastenbroek (1983) pointed out, likely accounts for
the absence of this species in the more northerly parts of Europe. He went on to
say that even southern Europe may not have provided the necessary conditions
for growth, and that the species may have occupied refugia in Northern Africa
during maximum ice cover. This issue cannot be resolved on the basis of the data
at hand.
2.3.5 Achillea (Asteraceae)
As part of an extensive series of studies on fl avonoids of members of Anthemideae,
Valant-Vetschera and Wollenweber (1988) examined the distribution of aglycones
in leaf exudates of members of the Achillea millefolium L. group of species. Both
qualitative and quantitative differences were noted for several species. An interesting
example involves differences that were noted among specimens of A. aspleniifolia
Vent. collected in Austria, Hungary, Romania, and Yugoslavia. Their observations
involved three O-methylated quercetagetin derivatives, the 3,6,4′-trimethyl ether,
centaureidin [71], the 3,6,7,4′-tetramethyl ether, casticin [72], and the 3,6,7,3′,4′pentamethyl
ether, artemetin [73] (see Fig. 2.19 for structures 71–73). The results
of their study are summarized in Table 2.4. This system might prove to be useful
in studying the action and control of O-methylation as has been done in Chrysosplenium
americanum by Prof. Ragai Ibrahim and his colleagues at Concordia
University in Montreal (e.g., De Luca and Ibrahim, 1985a, b).