The Geography of Phytochemical Races

6.4 Juan Fernandez Islands 271
when the data were used to construct a hybrid index. Flavonoid data were not useful in
this system owing to the high level of variation seen in the hybrid individuals. The area
surrounding Quebrada Villagra has been subject to considerable disturbance through
human activities and the pressures of grazing by both feral and domestic animals.
Within this area, the two Gunnera species have come into contact with resulting gene
exchange. No other instances of hybridization were found by those authors.
6.4.5 Peperomia (Piperaceae)
Peperomia Ruiz & Pavon is a large genus of approximately 1000 species (Mabberley,
1997, p. 540) distributed mainly in warm and tropical areas. In this section, we
consider four species that occur on the Juan Fernandez Islands, three endemics
plus one that also occurs on the South American mainland. The endemic species
are P. margaritifera Bert., from Masatierra, P. skottsbergii C. DC. from Masafuera
and P. berteroana Miq., which occurs on both islands. Peperomia fernandeziana
Miq. occurs on both islands and on the mainland. A detailed examination of the
fl avonoid chemistry of the island endemics, P. fernandeziana, and four additional
mainland species was conducted by Valdebenito et al. (1992a). The complex array
of compounds identifi ed included fl avones, C-glycosylfl avones, and fl avonols. The
fl avones were based on apigenin, acacetin, luteolin, luteolin 7-methyl ether, and
luteolin 4′- methyl ether (diosmetin) and were obtained either as aglycones, as glycosides,
or, in some cases, as sulfates. The C-glycosylfl avones, 19 compounds in
all, represented the major fl avonoid components. Comparison of the fl avonoid profi
les of the island species revealed signifi cant differences among them. Peperomia
margaritifera exhibited the simplest profi le characterized by a single fl avonol, three
C-glycosylfl avones, and the absence of fl avone O-glycosides. Peperomia berteroana
also had a depauperate C-glycosylfl avone profi le, but differed from P. margaritifera
in having a rich array of fl avone O-glycosides. Specimens of P. fernandeziana from
the Juan Fernandez Islands and from the mainland, though different in detail, were
suffi ciently similar in overall fl avonoid chemistry to suggest they are indeed the
same taxon. A particularly interesting observation, the signifi cance of which we
will see presently, was the fi nding that the pigment profi les of P. berteroana from
the two islands were different from each other with regard to fl avone O-glycoside,
C-glycosylfl avone, and fl avone sulfate profi les.
During their study of the Juan Fernandez endemic Peperomia, Valdebenito et al.
(1990a; 1992a) had opportunity to examine specimens of P. tristanensis Christoph.,
a taxon known only from Inaccessible Island in the South Atlantic. Inaccessible
Island is one of a small group that comprises the Tristan da Cunha Islands. This
group lies in the southern Atlantic Ocean at about 37°S, 12°W on the Mid-Atlantic
Ridge (Fig. 6.8). The group consists of three main islands, Tristan (0.5 million years
old), Inaccessible (2.9 million), and Nightingale (18 million), plus two lesser islets,
Middle and Stoltenhoff. (Gough Island, sometimes included with the Tristan group,
lies 350 km south–southeast of Tristan at 40°S, 10°W.)