The Geography of Phytochemical Races

3.1 North America 131
been found to occur naturally suggesting a close relation between the two. A third
rare, serpentine endemic in the Klamath area is the diploid A. cernua Howell.
Similar fl oral and leaf morphology suggest that A. cernua may have been derived
from A. cordifolia. The fl avonoid profi le of A. cernua, which consists of three compounds,
kaempferol 3-O-glucoside, quercetin 3-O-diglucoside, and quercetin 3-Ogentiobioside,
represents one of the most depauperate profi les in the subgenus. An
even more reduced profi le (only two compounds) has been reported from a rare
diploid population of A. cordifolia lending support to the possibility of a close
relationship between the two.
Arnica viscosa A. Gray, a diploid, is the rarest species in subgenus Austromontana.
It is known from only seven localities and appears to be restricted to volcanic
soil at high elevations. The fl avonoid profi le of this species is complicated by the
presence of several unique compounds: 5,6,7,3′-tetrahydroxy-4′-methoxyfl avone
[264]; 5,4′-dihydroxy-6,7,3′-trimethoxyfl avone (cirsilineol) [265]; and 3,5,7,4′tetrahydroxy-6,3′-dimethoxyfl
avone (quercetagetin 6,3′-dimethyl ether, spinacetin)
[266] (see Fig. 3.3 for structures 264–269). The structural features characterizing these
compounds, extra hydroxylation, and a moderate level of O-methylation, along with
the presence of compounds seen in several other species of subgenus Austromontana,
makes it diffi cult to do more than speculate on phylogenetic relationships, although
the authors (Wolf and Denford, 1984a) tend toward A. latifolia as the most likely
candidate. They conclude that it is probably the most recently derived species in the
subgenus occupying habitats that are less than 14,000 years old.
Fig. 3.3 Compounds 264–269, fl avonoids from Arnica viscosa