The Geography of Phytochemical Races

86 2 Examples Within Continents
Fig. 2.53 Map showing transects for Asclepias tuberosa fl ower color study
of plants with modest to higher levels of anthocyanin. The pattern of occurrence
of the color morphs was interpreted as arising from incomplete diffusion of an
adaptively superior complex of features, marked by the accumulation of anthocyanins,
outward from the assumed center of origin of the species, which was
taken as western Missouri and adjacent areas as listed above. The concentric
pattern has been broken from place to place, presumably by the lack of continuous
suitable habitats, resulting in widespread colonies that are subject to extreme
genetic bottlenecks. [Note that the conclusions in this paper were prepared by
Sewell Wright, to whom a copy of the manuscript had been sent by Woodson for
comment. Woodson never saw Wright’s comments, owing to the latter’s sudden
death. See Editor’s comments.] So far, as can be determined from Woodson’s
work, and the comments by Wright, no answer has been found to the question of
what selective advantage anthocyanin pigmentation might provide, although it is
altogether possible that this is only one part of a more complex set of features
that direct selection.
2.7.4 Phlox carolina (Polemoniaceae)
Phlox carolina L., a tall, perennial phlox native to southeastern United States, was
shown to exhibit a substantial degree of fl avonoid variation by Levy and Levin
(1975). In a subsequent paper, Levy and Fujii (1978) described attempts to establish
geographical patterns in the occurrence of leaf fl avonoids. Seventy-three collections
were made representing populations in Georgia, Alabama (a total of 64 populations),