The Geography of Phytochemical Races

2.7 North and Central America 81
2.7.2 Chenopodium fremontii (Chenopodiaceae)
Several species of weedy Chenopodium occur widely in western North America.
In an effort to gain a better understanding of some of these taxa, D. J. Crawford
and associates undertook an extensive biosystematic examination of the group. The
study represents an excellent example of the advantages to be gained by the application
of different techniques, including macro- and micromolecular methods, to
a complex system. The primary focus of this discussion is C. fremontii S. Watson,
which occurs over wide tracts in the southwestern states and shows wide ecological
amplitude occupying habitats that range from desert to montane sites. Extensive
morphological examination, including greenhouse studies, had established the
highly plastic nature of the species. These workers then turned to other methods in
order to estimate the level of genetic variation within the taxon. Their fi rst analysis
involved an examination of seed protein profi les of more than 210 individual
plants representing 33 populations; fi ve states were involved: Arizona, California,
New Mexico, Utah, and Wyoming (Crawford, 1976) (Fig. 2.51). Preliminary studies
had demonstrated that variation within populations was minimal and that plants
grown from seed from the same population exhibited invariant protein profi les;
morphological variation was maintained in cultivation, however. Fifteen of the 25
populations, in which plants were examined individually, showed only one protein
profi le; eight populations exhibited two protein profi les and two exhibited three
profi les. Numerical analysis of the data showed the existence of seven clusters with
identical protein profi les. The lowest level of similarity observed between any two
populations was 46%. It is useful to point out that C. fremontii is unusual in its variable
protein profi les compared to other related species whose profi les were shown
to be largely invariant: C. atrovirens Rydberg, C. desiccatum A. Nelson, C. hians
Standley, C. leptophyllum Nutt. ex Moq., and C. pratericola Rydberg (Crawford
and Julian, 1976).
Fig. 2.51 Map of Chenopodium fremontii sites