The Geography of Phytochemical Races

278 6 Oceanic Islands
the present context are three species of Ranunculus: one of which, R. moseleyi Hook. f.,
is endemic. The other two species, R. pseudotrullifolius Skottsberg and R. biternatus
Smith, are of circumpolar occurrence. A close relationship between these species had
previously been demonstrated through a cytogenetic study (Hennion and Couderc,
1993), in which all three were shown to be hexaploids with 2n = 48.
The cytogenetic study was followed by a detailed examination of the fl avonoid
profi les of the three species (Gluchoff-Fiasson et al., 1994), which revealed the presence
of a complex mixture of acylated quercetin di- and triglycosides. An example
of the sort of compounds identifi ed is quercetin 3-O-(caffeoylxylosylglucoside)-7-
O-glucoside [565] (see Fig. 6.13), which was observed as a major component of
both R. pseudotrullifolius and R. moseleyi, but present in only trace quantities in
R. biternatus. Clear distinctions among the taxa were thus possible based on the
degree of xylosylation seen in the respective taxa. The level of acylation observed
in each taxon also proved to be of value (Hennion et al., 1994). Glycosides bearing
xylose were predominantly seen in R. pseudotrullifolius and the endemic R. moseleyi,
in both of which it occurred in compounds that were marked as “abundant” or
as “major component.” Three xylose-containing glycosides were observed in
R. biternatus but were present as minor or trace components only. An analysis of
the HPLC peak areas for all compounds containing xylose showed highly discriminating
values, which the authors presented as “% xylosylation.” Four individuals
of R. biternatus averaged 1.1% xylosylation, with a range of 0.6–1.5%. Four individuals
of R. pseudotrullifolius and six of R. moseleyi gave values of 78.5% (range
58–91%) and 89.7% (range 86–94%), respectively. A similar calculation provided a
value for “% acylation.” A value of 84% (78–86%) was obtained for R. biternatus,
while values of 69.3% (range 64–81%) and 69.3% (range 46–77%) were obtained
for R. pseudotrullifolius and R. moseleyi, respectively. Further differences among
the three species were noted with regard to morphological characters and habitat.
In general, the comparatively narrower ranges of morphological variation for
R. pseudotrullifolius and R. moseleyi were very similar, whereas R. biternatus exhibited
a much wider range of structural variation as well as exhibiting a wider range
of variation in habitat ranging from aquatic sites to fell fi elds. Ranunculus pseudotrullifolius
and R. moseleyi are much more restricted in their choice of habitats
being almost entirely aquatic. The authors concluded that the combined results of
cytotaxonomic, morphological, chemical, and ecological examinations support a
comparatively recent colonization of the Kerguelen Islands by the two magellanic
species following the most recent glacial period, some 8000 years ago, followed by
differentiation of R. moseleyi from R. pseudotrullifolius.
Fig. 6.13 Compounds
560–564, anthocyanins from
Empetrum