The Geography of Phytochemical Races

116 2 Examples Within Continents
Chrysosplenium fi ts into several phytogeographic categories. In addition to the
local infraspecifi c differentiation just described, it also falls into the category of
genera with an eastern Asia–eastern North America–western North America distribution.
For example, several members of the opposite-leafed species of Chrysosplenium
occur in Japan with the group represented in North America by two
species, C. americanum Schwein. ex Hook., which occurs along the eastern seaboard
of North America, and C. glechomaefolium the western North American representative.
Evolutionary relationships between these two North American species
were discussed by Soltis et al. (1993) as part of a study of the genus using DNA
sequence data. Included in that study were two species native to extreme southern
South America, which will be discussed below under the category of polar disjunctions.
Eastern Asian–eastern North American disjunct taxa will also be discussed
later in this review.
2.7.20 Quercus rubra (Fagaceae)
Quercus rubra L., red oak, is a major component of the deciduous forests of eastern
North America, with a range that extends from Ontario south to the Gulf States
(Sargent, 1965). Part of the variability of the species has been formalized by the
recognition of var. borealis (Michaux f.) Farwell to account for trees in the northern
part of the species’ range, and at higher elevations in the southern Appalachians.
The two varieties, rubra and borealis, are thought to intergrade between 1200 m and
1350 m in the southern Appalachians.
An examination of the fl avonoids of red oak by McDougal and Parks (1984)
revealed altitudinal differences in the fl avonol profi les. One chemotype, characterized
by the presence of kaempferol [234] and quercetin 3-O-glycosides [235],
occurred in trees from lower elevations, whereas in trees from higher elevations
myricetin 3-O-glycosides [236] (see Fig. 2.71 for structures 234–236) were added to
the array. Mixed populations were observed between 600 m and 1050 m, somewhat
lower than the elevational range of overlap of the morphological varieties known to
grow between 1200 m and 1350 m (Sargent, 1965). The infl uence of environmental
and genetic factors on the expression of fl avonols in red oak was the subject of a
second paper by McDougal and Parks (1986). Acorns were collected from eight
sites representing an elevational gradient of 1455 m, divided equally, and planted in
nursery plots at 75–1140 m elevation. After 5 years, leaf samples were analyzed for
fl avonoids qualitatively and quantitatively. Regardless of the elevation of the nursery,
seedlings originating from high-elevation myricetin-positive trees retained their
capacity to synthesize myricetin, while seedlings from low-elevation nonmyricetin
stock continued to produce only kaempferol and quercetin derivatives. Quantitative
analyses indicated that the total amounts of fl avonoids varied somewhat with elevation,
but the array of compounds produced was not affected. Although the fl avonoid
chemotypes correspond to the two varieties of red oak in the southern Appalachians,
the zone of overlap of chemical and morphological characters does not agree.