The Geography of Phytochemical Races

132 3 After the Ice
The last species in this group, Arnica nevadensis A. Gray, is interesting in that
it exhibits pappus features characteristic of other subgenera, in addition to features
suggesting that it has been derived from A. cordifolia. Flavonoid evidence
supporting its placement in subgenus Austromontana comes from the presence of
a suite of quercetin glycosides common to most other species. Luteolin 4′-methyl
ether (diosmetin) [267] and 6-methoxyluteolin (nepetin), the aglycone of [253],
however, are unique to A. nevadensis. Sampling was not suffi cient to establish
whether these compounds are characteristic of the Klamath populations.
The general conclusion drawn by Wolf and Denford (1984a) concerning subgenus
Austromontana is that A. cordifolia, with its more primitive morphology, cytology,
wide geographical distribution, and fl avonoid profi le, represents the ancestral species.
Differentiation into the other species is thought to have occurred primarily in
the Klamath area resulting in the establishment of four local, edaphically specialized
endemics (A. spathulata, A. venosa, A. cernua, and A. viscosa) and three other
species whose ranges have expanded to greater or lesser degrees.
A separate example of a group of diploid species centered in the Klamath
region, with apparent radiation from the center involves Sedum section Gormania
(Crassulaceae). The section consists of 12 taxa that occur in western Oregon and
northern California. A study of the fl avonoids of all members of the section (Denton
and Kerwin, 1980; see also Denton, 1979) revealed the presence of three compounds,
two of which were identifi ed as a kaempferol 3,7-di-O-glycoside [268] and
3,5,7,3′,4′-pentahydroxy-5′-methoxyfl avone (laricytrin) [269]. The third compound
was identifi ed only as an O-methylated fl avone derivative. All 12 taxa exhibited the
fi rst two compounds, but the presence of the fl avone derivative allowed defi nition of
two geographical groups with only slightly overlapping ranges. Six species, S. laxum
(Britton) Berger (four subspecies), S. moranii, R. T. Clausen, S. oblanceolatum
R. T. Clausen, and S. oregonense (Wats.) Peck identifi ed as group a, occur in
the Cascade Mountains of Oregon and in the Klamath Mountains of Northwestern
California. Sedum albormarginatum R.T. Clausen and S. obtusatum A. Gray (four
subspecies), identifi ed as group b, occur primarily in the Sierra Nevada Mountains
in California with only a small overlap into the Klamath area. The authors suggested
that the capacity to make the fl avone was lost with migration from a center of origin
in the Klamath Mountains (group a taxa) eastward and southward. There appears to
be no relationship between fl avonoid chemistry and ploidy level (diploids and polyploids
are known in each group).
We can return now to the observations on the last group of Arnica species, the
edaphic specialists. Wolf and Denford’s (1984a) observations are in general agreement
with hypotheses concerning endemism in Parthenium (Mears, 1980b). The
fl avonoid chemistry of all North American members of Parthenium (Asteraceae)
was studied by Mears (1980a), who recorded the occurrence of 34 compounds that
were about equally divided between aglycones and glycosides. Species enjoying
wide ranges of occurrence on a variety of noncalcareous substrates tend to accumulate
larger arrays of compounds, owing primarily to glycoside diversity. Species
limited to limestone or gypsum-based substrates, on the other hand, tend to have
much simpler pigment profi les with O-methylated aglycones as the predominant