The Geography of Phytochemical Races

4.1 Across the Atlantic Ocean 175
Fig. 4.2 Map of Datisca
glomerata “plastones.” Populations
are identifi ed as PG-N
from the north and central
parts of the state, and PG-S
from southern California and
northern Baja California.
PG-N’ represents a variant on
the northern form
calaminaria from zinc-lead alluvial deposits along the River Tyne in northeastern
England, which are very similar to plants growing near Aachen, Germany, the latter
representing the “Continental metal” form.
Lauranson et al. (1995) investigated the fl avonoid profi les of populations
representing the range of the species. Compounds identifi ed were mono- and
diglycosides of the widespread fl avonols: kaempferol, quercetin, isorhamnetin, and
myricetin, “polyglycosides” of quercetin and myricetin, and caffeic acid derivatives
(chlorogenic acids?). Seven different profi les (combinations) of these compounds
were observed in plants from the fi ve main parts of the range: maritime
Europe (seven profi les), Continental metallicolous (three profi les), British metallicolous
(two profi les), Arctic and subarctic (three profi les), and North American
West Coast (two profi les). Earlier studies of allozyme variation revealed patterns
that are in close agreement with the fl avonoid results (Vekemans, 1992; Vekemans
et al., 1992). Twenty alleles representing fi ve loci in European plants contrasted
with the almost total monomorphic situation observed in plants from California.
Within California, differences in allozyme profi les were observed among populations,
suggesting that local factors may exert signifi cant infl uence on genetic
structure as well. There has also been a change of breeding system in this species,
from outcrossing in Europe to total or nearly total self-compatibility in populations
in North America. Those workers suggested that the limited variation seen in
North American populations was likely the result of the founder effect following
long-distance dispersal.