The Geography of Phytochemical Races

268 6 Oceanic Islands
It is not possible to do much more than speculate on this problem, but some additional
information might help to shed some additional light on the subject. In particular,
a rigorously supported DNA phylogeny should tell if E. fernandezianus made
the trip from the mainland to the islands independently, that is, Erigeron on the Juan
Fernandez Islands is not monophyletic. Unfortunately, no macromolecular studies
appear to have been done on this set of species (T. F. Stuessy, personal communication).
If the genus on the islands should prove to be monophyletic, and the route of
evolution suggested by morphology is correct, then a study of the genes controlling
fl avonoid biosynthesis could provide important clues as to how these processes are
moderated. It would, of course, be interesting to learn if some ecological factor is
involved in the turning-off and turning-on processes.
6.4.4 Gunnera (Gunneraceae)
Gunnera L., the sole genus of Gunneraceae (at one time considered part of
Haloragidaceae), consists of perhaps 40 species (Mabberley, 1997, p. 319). Members
of Gunnera occur mainly in the Southern Hemisphere, with representatives known
from the Hawaiian Islands and as far north as southern Mexico. Perhaps the most wellknown
member of the genus is G. chilensis Lam., which is often found as a decorative
plant owing to its spectacularly large leaves. We are concerned in this chapter with
three species of Gunnera endemic to the Juan Fernandez Islands: G. bracteata Steud.,
G. masafurae Skottsb., and G. peltata Phil., and possible ancestors on the South
American mainland. A further distinction can be made with the island endemics:
G. bracteata and G. peltata are endemic to Masatierra, while G. masafuerae, as its
name implies, is known only from Masafuera, the younger island. Vegetative and
morphological characteristics of mainland Gunnera (belonging to subgen. Panke)
suggested G. tinctoria (Mol.) Mirb. as the most likely ancestral candidate for the
island endemics. Identical chromosome counts (n = 17) for the island taxa and for
G. tinctoria lend further support for this idea (Pacheco et al., 1993).
A detailed study of the fl avonoid chemistry of the island endemics, the closely
related G. tinctoria, and fi ve additional species from the mainland provided
additional evidence pointing toward G. tinctoria as the ancestral species (Pacheco
et al., 1993). The fl avonoid profi les of all species consisted of fl avonol glycosides
as major components with an unidentifi ed fl avone glycoside and several unidentifi
ed phenolic compounds (presumably not fl avonoids). The pattern of distribution
of the fl avonol glycosides and unidentifi ed fl avones within the set of nine
species proved to be extremely informative. (The phenols were ubiquitous and
are not considered further.) Kaempferol glycosides were seen in neither the
island species nor G. tinctoria, but were present, in several combinations, in
the rest of the mainland taxa. The isorhamnetin glycosides showed the reverse
pattern, with one exception: the island endemics and G. tinctoria exhibited
these compounds, whereas four of the other mainland species did not. The sole
exception is G. boliviari, which exhibited one of the isorhamnetin derivatives.