The Geography of Phytochemical Races

276 6 Oceanic Islands
primarily of O-glycosides of the fl avonols, quercetin and isorhamnetin (quercetin
3′-methyl ether), along with C-glycosyl derivatives of the fl avones, apigenin
and luteolin (Chang and Jeon, 2003). This profi le is very similar to what has been
recorded for other species of Cotoneaster in Asia. This led the authors to conclude
that, as in the case of other woody plants growing on the island, very little change
in either morphology or chemistry has occurred during the species’ existence on the
island.
6.7 Tristan da Cunha and the Falklands
6.7.1 Empetrum (Empetraceae)
This example involves the Tristan da Cunha Archipelago, the Falkland Islands
(Islas Malvinas), and mainland South America (Fig. 6.8); the plant in question is
Empetrum rubrum Vahl ex Willd. This is one of two or three species that constitute
Empetraceae (Mabberley, 1997, p. 255); the others are the circumboreal E. nigrum
L. and E. eamesii Fernald & Wiegand (considered by those authors as a segregate
from E. nigrum). The taxonomic history of the genus was reviewed in D. M. Moore
et al. (1970).
As part of a chemotaxonomic study of the family, Moore et al. (1970) examined
the fl avonoid profi les of 18 populations of E. rubrum, 16 ranging from the Chilean
Andes to southeastern Fuegia, and one each from the Falkland Islands and Gough
Island in the Tristan da Cunha group (Fig. 6.8). (The species also occurs on the Juan
Fernandez Islands but was not sampled from there.) Many compounds (spots) were
observed on chromatograms, six of which were identifi ed as quercetin, 3-Oarabinoside,
3-O-galactoside, and 3-O-rutinoside; gossypetin, 3-O-galactoside
(gossypetin is 8-hydroxyquercetin); and two hydroxycinnamic acid derivatives.
Additional fl avonoids were among the group of unidentifi ed spots. Chromatographic
analysis of the unusual black-fruited E. rubrum revealed the same pigment
array as normally found in the black fruits of E. nigrum, namely, glycosides of
petunidin [560], cyanidin [561], peonidin [562], delphinidin [563], and malvidin
[564] (see Fig. 6.12 for structures 560–564). Normal red-fruited E. rubrum lacked
pigments having a trisubstituted B-ring (delphinidin and malvidin) and had only
glycosides of cyanidin and peonidin.
Although not the main issue here, it is interesting to note that fl avonoid profi
le variation in the Northern Hemisphere members of Empetrum shows no correlation
with geography, regardless of whether E. nigrum is taken in the broad
sense, or whether one recognizes E. eamesii as well. The situation with regard to
E. rubrum is somewhat different in that some geographical patterns are evident, as
is seen in the case of quercetin 3-O-rutinoside (commonly known as rutin) (identifi
ed as F3 in that work). Rutin is a common constituent of E. nigrum, including
E. eamesii, but was observed only rarely in specimens of E. rubrum. However, rutin