Analysis of systematic and phyletic relationships among alveolate-fruited Chenopodium of western North America

Abstract

A biosystematic analysis of the western North American alveolate-fruited Chenopodium (subsect. Cellulata) was undertaken to examine the taxonomy and evolutionary relationships within and among the three diploid species C. neomexicanum, C. palmeri, C. watsonii and the tetraploid C. berlandieri. Numerical taxonomic analysis of morphological characters demonstrated that the four species are distinct with respect to leaf and fruit characteristics. Of the three diploid species, C. neomexicanum showed the closest morphological similarity to the tetraploid. Three morphological elements were identified within the tetraploid population system. Numerous morphological characters showed strong altitudinal gradients for populations of C. berlandieri. The greatest amount of morphological variability for the tetraploid population system occurred in the southwestern United States and northern Mexico; this is also the area where the three diploid species come into contact. A comparison of the data obtained from the morphological and isozymic analyses appeared to show little concordance for the tetraploid population system. Both sets of data, however, demonstrated similar centers for greatest variability for the populations of C. berlandieri. Taking into consideration the results obtained from both types of analyses, an evolutionary history of C. berlandieri is proposed. The tetraploid appears to have had a center of origin in the southwestern United States. Populations radiated northward from this center into the Rocky Mountains and east to the Great Plains, southward onto the central Mexican Plateau, and eastward to east Texas and along the Gulf Coast. On the basis of morphology, electrophoretic banding patterns, and geographical ranges, C. neomexicanum and either C. watsonii or a now extinct diploid are suggested as being the ancestors to the tetraploid.