The Geography of Phytochemical Races

4.3 North Pacifi c 197
this magnitude suggests that the South American species, or an ancestor, got to their
present locations by means of long-distance dispersal. Whether this disjunction
occurred as a result of direct long-distance dispersal from eastern Asia, or whether
it represents the results of migration from Asia and then southward migration along
the western Cordillera of North and South America, with subsequent disappearance
of intermediate populations, cannot be resolved from the available data. Neither is
it possible to say when dispersal might have occurred. Whether it was an ancient or
comparatively recent event cannot be estimated with any degree of certainty at the
moment, owing to the lack of a reliable “clock” for matK divergence.
With the suggestion that the South American species are not ancestors, it is possible
to comment on the evolutionary history of the fl avonoid profi les of the genus. Instead
of the depauperate fl avonoid profi le of C. valdivicum representing the ancestral condition,
it would now appear that the simple array of pigments resulted from loss of some
biosynthetic capacities. Several changes appear to have occurred: (1) reduction in
overall level of substitution, that is, number of hydroxyl groups; (2) loss of the capacity
to effect 2′-hydroxylation, which appears to be a feature of sect. Oppositifolia to
which the species belongs; and (3) possible change in the level of O-methylation. The
apparent loss of 2′-hydroxylation requires some comment. Although 2′-hydroxylation
appears to be limited to members of sect. Oppositifolia, not all members of the section
have been examined for fl avonoids. Thus, it is entirely possible that some member
of that section, which could not form 2′-hydroxyfl avonoids, gave rise to the ancestral
South American taxon. The third point, having to do with lower level of O-methylation,
may simply be a ramifi cation of the fi rst listed change, that is, fewer substitutions on
the fl avonoid nucleus provide fewer sites for O-methylation.
The relationships between the North American species of sect. Oppositifolia and
their closest relative in Japan led Soltis et al. (2001) to an interesting conclusion.
The observation that the eastern and western North American species emerged as
a monophyletic group parallels the fi nding with other taxa that share the eastern
North America–western North America–eastern Asian disjunction. The same pattern
of relationships was observed in a study of Aesculus (Hippocastanaceae, horse
chestnuts) (Xiang et al., 1998a) and members of several other genera, including
Aralia sect. Aralia, Boykinia, Calycanthus, Cornus, Tiarella, and Trautvetteria
(Xiang et al., 1998b). In all of these, the North American members are monophyletic,
suggesting that the eastern North American member of each set is more closely
related to the western North American member than it is to the eastern Asian member.
This contrasts with the classical view (Gray, 1846) that the eastern Asian and
eastern North American members of a species pair are most closely related.
4.3.6 Iris setosa (Iridaceae)
Iris setosa Pallas occurs widely in subarctic parts of the Northern Hemisphere.
Several varieties of I. setosa have been recognized over the years: var. canadensis
M. Foster (syn. I. hookeri Penny) in the Canadian north, and vars. setosa, nasuensis