The Geography of Phytochemical Races

7.3 Chrysosplenium (Saxifragaceae) 289
Blennosperma nanum var. robustum lacked the fl avone, but exhibited the fl avonol
glycosides plus cyanidin 3-O-monoglycoside [structure 561] in some individuals.
7.3 Chrysosplenium (Saxifragaceae)
Chrysosplenium enjoys a distribution that qualifi es it for inclusion in several categories
in this review. Members are known from northern Europe, North America,
eastern Asia (principally Japan), and extreme southern South America. The similar
fl avonoid chemistry of the eastern North American–western North American species
pair C. americanum and C. glechomaefolium was mentioned earlier, along
with comments on apparent fl avonoid differences between sections Alternifolia
and Oppositifolia.
Of interest here is the one South American species (there are two) for which
we have some fl avonoid data (Bohm and Collins, 1979). Analysis of a specimen
of C. valdivicum W. J. Hooker afforded four compounds, three of which
yielded isorhamnetin, glucose, and rhamnose on total hydrolysis and isorhamnetin
3-O-glucoside on partial hydrolysis, suggesting the presence of rhamnosylglucosides,
for example, [590] (see Fig. 7.3 for structures 590–601). The fourth
compound was identifi ed as kaempferol 3-methyl ether [591]. There was no
indication of the more highly substituted fl avonols isolated from other Chrysosplenium
species, that is, compounds possessing extra hydroxylation on both
the A- and B-rings and O-methylation, for example, 5,2′-dihydroxy-3,7,4′,5′tetramethoxyfl
avone [592], a compound known from C. grayanum, one of the
Asian species. The pattern observed in C. valdivicum is the simplest array of
fl avonols reported from any member of the genus, and thus could be taken as
support for Hara’s (1957) view that C. valdivicum, with its array of “archaic”
features, resembles the prototype of the genus. Following O. R. Gottlieb’s (1986,
1990) ideas concerning level of oxidation and degree of “advancement” of a
fl avonoid profi le, the picture we see in the C. valdivicum is of a set of compounds
with an oxygenation pattern characteristic of the basic fl avonoid structure,
compared to the more complex fl avonoids from the genus that have extra
oxygenation on both the A-ring (6-oxygenation) and B-ring (2′-oxygenation),
and in several cases both. The diffi culty with this interpretation, as pointed out
by Gornall and Bohm (1978), is that a simple oxygenation pattern may also be
arrived at by loss of biosynthetic capabilities, and thus represent a derived, or
specialized, situation.
A recent phylogeny of the genus (Soltis et al., 2001) revealed that the South
American taxa are most closely related to species from eastern Asia. In terms of
fl avonoid profi les, this requires us to reappraise the signifi cance of the simple
compounds. Thus, as suggested above, the simple fl avonoid glycoside profi le of
C. valdivicum appears to represent a loss of biosynthetic capacities, in particular,
extra oxygenation, and not a simple profi le to which structural features were added
in later stages of evolution.