The Geography of Phytochemical Races

196 4 Intercontinental Disjunctions
O-methylation. A particularly interesting observation is that members of the alternateleafed
group (Franchet’s sect. Alternifolia) accumulate a variety of fl avonols, among
which are several characterized by the presence of 6-oxygenation, for example,
C. tetrandrum (Bohm et al., 1977), while the opposite-leafed group (Franchet’s sect.
Oppositifolia) accumulate a similar array of compounds along with fl avonols that
feature oxygenation at C-2′. As per the author, 2′-oxygenated fl avonoids have so
far been reported only from opposite-leafed species, although about half of the species
in Chrysosplenium have not been thoroughly examined or, in many cases, not
examined at all for fl avonoids. As the examination of C. glechomaefolium revealed,
not all members of an opposite-leafed species necessarily have these compounds,
although most appear to be capable of making the 6-oxygenated fl avonols (but see
C. valdivicum below for an important exception). However, C. americanum (Collins
et al., 1981) from the eastern North America, C. glechomaefolium (Bohm and Collins,
1979) from the western United States, and several opposite-leafed species from Japan
(Jay and Voirin, 1976; Arisawa et al., 1991, 1992, 1993a, b, 1997, and earlier work
by Morita and co-workers cited therein) accumulate 2′-oxygenated fl avonoids.
There have been several suggestions above that the signifi cance of relationships
based on secondary metabolites can only be assessed when phylogenetic relationships
within the taxon in question have become established. A paper by Soltis et al.
(2001) has now provided the opportunity to do just that. Sequence information from
the matK gene was obtained for 28 species (33 collections) representing 13 of the
17 series of the genus defi ned by Hara (1957). The data were subjected to phylogenetic
analysis, from which two main clades emerged that corresponded to the two
groups of species recognized by Hara as sections Oppositifolia and Alternifolia.
Further, the analyses revealed that eastern Asia was the most likely area of origin
of the genus and that differentiation into the two groups was a comparatively early
event in its evolutionary history and that it is likely to have preceded major dispersal
events. Subsequent divergence of the alternate-leafed group yielded two subgroups,
one of which comprises taxa native to the Himalayan region, and one that
comprises Japanese species plus the two circumboreal species C. alternifolium L.
and C. tetrandrum Makino. At least one migration out of eastern Asia was necessary
to account for the establishment of the circumboreal taxa. The clade comprising
sect. Oppositifolia consisted of three subclades: (1) Asian species; (2) two
Asian species (C. ramosum Maxim. and C. delavayi Franch.) in addition to one
of the South American species (C. valdivicum Hook.); and (3) a group of species
that occurs in Asia (C. grayanum Maxim. and C. pseudofauriei H. Lev.), Europe
(C. oppositifolium L.), and North America (C. americanum Schwein. ex Hook. and
C. glechomaefolium Nutt. ex Torr. & A. Gray). The North American species are sisters,
and together are the sister to the European species. In turn, the North American
and European species constitute the sister group to the Asian species. This set of
relationships requires a second migration out of eastern Asia.
Hara (1957) considered the South American species, C. valdivicum and
C. macranthum Hook., to be ancestral in the genus. This was not borne out by
the matK sequence data. Rather, C. valdivicum (C. macranthum was not studied),
emerged as part of a clade consisting otherwise of Asian species. A disjunction of