The Geography of Phytochemical Races

4.5 Western Pacifi c: Eastern Asia, Japan, and the Philippines 215
Table 4.8 Percentage fl avonoid aglycone occurrence in species of Rhododendron sect. Vireya
(from Harborne, 1986)
Flavonoid Southeastern Asia Malesian-Australian region North America
Quercetin 100 94 100
Myricetin 51 35 35
Kaempferol 23 44 82
Azealatin 34 15 12
Caryotin 10 4 12
Gossypetin 76 0 0
Dihydrofl avonols 68 13 18
Species studied 206 52 18
differences in pollination vectors. This would be in line with the morphological differences
that characterize members of this section as well. Harborne went on to point
out that the most signifi cant feature of the survey is the correlation of pigment profi
les with geography. The differences in profi les between species from southeastern
Asia and those from the Malesian-Australian region are similar to the differences
between the profi les in southeastern Asian species and North American species.
These differences support the view that the genus originated in southeastern Asia,
the Himalayas, or central China, and radiated outward from there. The species from
the Malesian-Australian region would represent one set of derived species, and
another from North America. Much additional work is needed to put these speculations
on fi rmer ground. Needless to say, this would seem an excellent system in
which to examine phylogenetic relationships using gene-sequence data.
4.5.4 Gesneriaceae
Gesneriaceae is a large tropical and subtropical family, many members of which
are prized for their spectacular and commercially important fl oral displays, for
example, Gesneria, Gloxinia, Saintpaulia, Sinningia, and Streptocarpus. The family
is of interest to us here owing to chemical differences between the two major
subfamilies, Gesnerioideae, primarily a New World taxon with representatives in
southeastern Australasia (hence, its rather arbitrary inclusion in this section), and
Cyrtandroideae, which is an Old World taxon. An unusual feature of the colored
pigments of a Gesneria species was fi rst reported by Robinson et al. in 1934, who
identifi ed an anthocyanidin derivative that lacked the hydroxyl group normally
present at C-3. The compound, apigeninidin [384], which belongs to a class of
compounds referred to 3-deoxyanthocyanidins, can be compared to the normal
anthocyanidin pelargonidin [385] (see Fig. 4.20 for structures). The B-ring deoxy
analog, luteolinidin [386], was discovered in a member of Gesneriaceae some years
later (Harborne, 1960). A subsequent survey (Harborne, 1966), reported detection of
3-deoxyanthocyanins in 18 species representing 11 genera of Gesnerioideae. From
that same work we also learned that these pigments were absent from 25 species