The Geography of Phytochemical Races

194 4 Intercontinental Disjunctions
3-O-glycoside would be formed fi rst. Alternatively, it might simply be the product
of the 7-O-glucosyltransferase operating on quercetin rather than on one of the
quercetin 3-O-monoglycosides. The key feature in these observations is the presence
of the 3,7-diglycosylation products instead of 3-O-diglycosides in Cladothamnus.
These results were discussed in terms of “diglycoside replacement,” where it
was concluded that the set of compounds involved represented the operation of
enzymes that characterize this genus (or species, depending upon one’s taxonomic
view). It seems reasonable to suggest that this level of glycosylation represents a
derived situation relative to the more common sequence of two glycosylations at
position-3 of the fl avonols (one on the fl avonoid hydroxyl group and a second on
one of the sugar hydroxyl groups), although again the matter of the need for a reliable
phylogeny arises. At any rate, the occurrence of these compounds clearly sets
this taxon off from the others. The other three taxa also are distinguishable from
each other on the basis of their respective glycosylation patterns.
4.3.4 Tiarella (Saxifragaceae)
Tiarella consists of three species, T. cordifolia L., which grows widely in eastern
North America; T. polyphylla D. Don, which is native to eastern Asia; and the western
North American T. trifoliata L. Tiarella trifoliata is considered by some to comprise
three varieties based upon leaf morphology: var. trifoliata, var. unifoliata, and var.
laciniata. The fl avonoid profi les of these three species of Tiarella were found to be
based upon the common fl avonols, that is, kaempferol, quercetin, and myricetin,
and the fl avone luteolin (Soltis and Bohm, 1984). The glycosidic derivatives identifi
ed included 3-O- and 7-O-mono-, 3-O- and 3,7-di-O-, and 3-O-triglycosides of
the fl avonols, and a 7-O-glucoside of the only fl avone observed, luteolin. Picman
and Bohm (1982) had described the fl avonoid profi les of the T. trifoliata complex
(all varieties). The distribution of compounds in the three species is presented in
Table 4.4. The only compounds held in common by the three species are kaempferol,
quercetin, and myricetin 3-O-glucosides and quercetin 3-O-rutinoside.
All other compounds exhibited variable occurrences and apparent concentrations
(estimated by chromatographic spot size). Tiarella polyphylla displayed the simplest
profi le, which consisted of only six compounds. Tiarella trifoliata exhibited the most
complex profi le, lacking only the 3-O-rhamnosides and triglycosides of quercetin
and myricetin.
The glycoside profi le of T. trifoliata was the most complex of the three taxa
in its possession of fl avonol 7-O-glucosides, 3,7-di-O-glucosides, and the fl avonol
3-O-glucosylxylosides. It is interesting to note that the array of fl avonoids reported
from Asian members of tribe Cladothamneae (Ericaceae) is also the simplest of the
four taxa involved in that study. In contrast, Vogelmann (1983) observed simpler
fl avonoid profi les in North American members of the genus Agastache (Lamiaceae)
compared to the Asian counterparts.