The Geography of Phytochemical Races

3.1 North America 133
structural type. The possible function of fl avonoids as antiherbivore defense compounds
was discussed, but Mears (1980b) found no correlation between complexity
of fl avonoid profi le and latitude, as might be the case if complexity of profi le
increases as one goes from temperate to more tropical climates with concomitant
increase in insect predators. Although the number of samples studied was not large,
there was a relationship between latitude and complexity of pigment profi les in taxa
restricted to calcareous substrates. No driving force for this apparent relationship
is evident.
Returning to our consideration of North American Arnica, we look next at the
fl avonoid studies of subgenus Arctica (Downie and Denford, 1986b). The fi rst taxa
to be studied by those workers were A. frigida Meyer ex Iljin subsp. frigida, which
occurs in eastern Siberia, Alaska, the Yukon, and in a few sites in northern British
Columbia; A. frigida subsp. griscomii (Fernald) S. R. Downie, restricted to the
Gaspé Peninsula (Quebéc) and northwestern Newfoundland; and A. louiseana Farr,
which occurs at high elevations in the Rocky Mountains of Alberta and British
Columbia (this taxon was previously considered as a subspecies of A. frigida; taxonomic
revision by Downie and Denford, 1986a). Arnica frigida subsp. frigida consists
of three chromosome races with 2n = 38, 57, and 95, while A. frigida subsp.
griscomii and A. louiseana both have 2n = 76. The signifi cance of these numbers
can be appreciated by noting Barker’s (1966) observation that no well-developed
sexual species occur in glaciated areas, and that no polyploid taxa appear to occur
in unglaciated areas. Downie and Denford (1986a) established that populations of
A. frigida from unglaciated areas, in fact, reproduced sexually.
The second paper from these workers (Downie and Denford, 1986b) concerned
the application of fl avonoid data to relationships among the three subspecies. The
pigment profi les were straightforward consisting of the 3-O-mono- and diglycosides
of kaempferol and quercetin and luteolin 7-O-glucoside. Individual profi les ranged
from two to six compounds. Quercetin 3-O-galactoside and 3-O-diglucoside were
observed in all specimens studied; all other compounds varied to a greater or lesser
degree. The key observation from this study is the high degree of similarity between
western subsp. frigida and eastern subsp. griscomii: the profi le of the Québec population,
consisting of kaempferol 3-O-glucoside, quercetin 3-O-galactoside, and 3-Odiglucoside,
was identical to four 2n = 38 populations from Alaska and three 2n = 57
populations from each Alaska and the Yukon. The Newfoundland profi le (two populations)
was identical to the profi le from eight 2n = 38 populations from Alaska, as
well as three 2n = 57 populations from the Yukon. The close morphological similarity
between the two subspecies suggests that they may be remnants of a once transcontinental
distribution that became disrupted by Pleistocene ice, and that eastern
and western members survived in glacial refugia with subsequent expansion of the
western component. The observation that the fl avonoid profi le of subsp. griscomii
falls within the limits of the profi le observed for subsp. frigida adds further weight
to this suggestion. It was not possible to draw any fi rm conclusion as to whether
A. louiseana, the Rocky Mountain member of the group, represents the product
of some hybridization event or whether it, or an ancestor, also survived glaciation.
The authors concluded by pointing out the need for studies of genetic variation