The Geography of Phytochemical Races

6.4 Juan Fernandez Islands 265
(fl avonol) derivatives were not seen in any of the species of subgen. Phoenicoseris.
Other differences are relatively minor, accountable by operation (or lack thereof)
of a single enzyme. For example, all four species in subgen. Dendroseris appear
to be unable to make apigenin diglucosides, but at least some of the members of
the other two subgenera can. However, without knowing precisely what the structures
of these compounds are, it is impossible to draw any conclusions. It is useful
to note, however, that each of the Masafueran species exhibits a fl avonoid profi le
closely resembling at least one of the species from the respective subgenera from
Masatierra. At most, there would appear to be single enzyme differences involved.
In an effort to locate a likely, or at least possible, mainland ancestral type, these
workers determined the fl avonoid profi les of representatives of a number of candidate
genera. Their results pointed to Hieracium and Hypochaeris as possibilities,
with their choice going to a species of the former from Chile. More recent work
using macromolecular techniques suggested closer ties to Sonchus s.l., or possibly
Embergeria from New Zealand (Bohm, 1998b, p. 252; parenthetical remark
added by T. F. Stuessy, volume editor). It is prudent to point out that, even with
detailed fl avonoid chemistry of possible ancestral taxa, comparatively few additional
insights would be gained owing to the simple and homogeneous fl avonoid
chemistry of these genera (Bohm and Stuessy, 2001).
Insights into evolutionary relationships of Dendroseris have been gained through
application of macromolecular tools. The morphological studies of Sanders et al.
(1987) provided the background for all subsequent investigations, fi rst by uniting
in one genus the 11 taxa that had, prior to then, been dispersed in four genera, and
then by providing the fi rst explicit phylogeny of the genus. Electrophoretic patterns
within the genus were studied by Crawford et al. (1987), who found comparatively
low level of genetic variation compared to other insular endemics (De Joode and
Wendel, 1992). Esselman et al. (2000) described a study of random amplifi ed polymorphic
DNA (RAPD) markers, while a study by Crawford et al. (1992a) involved
a restriction-site analysis of chloroplast and nuclear ribosomal DNA. Although four
species were missing from that work, owing to limited quantities of plant material,
results were encouraging in that the emerging phylogeny was very similar to that
obtained from the other data sets. The sampling problem was partially overcome
when Sang et al. (1994) employed the polymerase chain reaction (PCR) technique
to amplify DNA (using internal transcribed spacer (ITS) region of nuclear ribosomal
DNA) making it possible to include two additional species. Again, subgenera
Dendroseris and Phoenicoseris emerged as strongly supported clades. The situation
with regard to members of subgen. Rea is less straightforward.
6.4.2 Robinsonia (Asteraceae)
Robinsonia (Asteraceae: Senecioneae), the second largest endemic genus on the
islands, consists of seven species assorted into two subgenera, subgen. Rhetinodendron,
consisting solely of R. berteroi (Hemsl.) Sanders, Stuessy & Marticorena