ALLOZYME VARIATION IN SEVERAL CLOSELY RELATED DIPLOID SPECIES OF CHENOPODIUM OF THE WESTERN UNITED STATES

Twelve allozyme loci were examined in a complex of closely related diploid (2n = 18) members of the genus Chenopodium occurring in the western United States. These plants are generally treated taxonomically as belonging to C. atrovirens, C. desiccatum, C. hians, C. leptophyllum, and C. pratericola. Also included were populations referable to C. incognitum. The enzymes examined and the allelic designations are given as follows: leucine aminopeptidase, Lap; phosphoglucoisomerase, Pgi-J, Pgi-2; glutamate-oxaloacetate transaminase, Got-i, Got-2, Got-3; glutamate dehydrogenase, Gdh; phosphoglucomutase, Pgm-J, Pgm-2; malate dehydrogenase, Mdh-l, Mdh-2; and malic enzyme, Me. All populations were fixed for the same allele at Gdh, Pgi-2, and Mdh-1. Chenopodium hians was fixed for a unique allele at Got-3 and contained two alleles at the Lap locus and two at Pgi-l which were not detected elsewhere. Chenopodium leptophyllum likewise has unique alleles at Lap and Pgi-I. The other three taxa, C. atrovirens, C. desiccatum and C. pratericola, have alleles at Lap and Pgi-J which were not found in C. hians or C. leptophyllum. The former three species have the same alleles in highest frequency at all polymorphic loci except Me, where C. desiccatum is consistently separable from C. atrovirens and C. pratericola. Allozyme data are concordant with information from morphology, flavonoid chemistry and seed protein profiles in suggesting that: (1) Chenopodium hians and C. leptophyllum are best regarded as distinct species; (2) C. atrovirens and C. pratericola are very similar and perhaps should not be recognized at the specific level; (3) C. desiccatum appears most closely allied to C. pratericola; (4) plants referable to C. incognitum represent two biological entities, one the same as C. atrovirens, and the other conspecific with C. hians; (5) little genetic variation is detectable in any taxon of these weedy annuals; (6) interspecific hybridization is not a cause of taxonomic difficulties in these plants. THIS PAPER reports the results of a study of allozyme variation in a complex assemblage of diploid (2n = 18) members of the genus Chenopodium occurring in the western United States. These plants have been treated in various ways taxonomically, with the recognition of from two (Hitchcock and Cronquist, 1964) to five species (Wahl, 1952-53; Crawford, 1975). Although Wahl and one of us (D. C.) each recognized five species, we are not in complete agreement. Wahl (1952-53) recognized the following taxa in this complex: (1) C. atrovirens Rydberg; (2) C. desiccatum A. Nelson var. desiccatum; (3) C. desiccatum A. Nelson var. leptophylloides (Murr.) Wahl; (4) C. hians Standley; (5) C. incognitum Wahl; and (6) C. leptophyllum Nutt. ex Moq. Crawford (1975) chose to treat C. desiccatum var. leptophylloides as a species (C. pratericola I Received for publication 27 January 1978; revision accepted 13 October 1978. Research supported by NSF grants GB-29793X, BMS 7421384 and DEB 78-15360 to D. J. Crawford. Appreciation is expressed for support from the College of Arts and Sciences, University of Wyoming, with special thanks to Drs. E. G. Meyer and E. B. Jakubauskas. B. A. Schaal provided critical comments on the manuscript. Rydberg) and did not recognize C. incognitum as a distinct taxon. Instead, he referred members of this species to C. atrovirens or C. hians, and thus viewed it as being comprised of two distinct taxa. Previous studies on the complex have included morphology, somatic chromosome karyotypes, flavonoid chemistry and seed protein profiles (Crawford and Reynolds, 1974; Crawford, 1975; Crawford and Julian, 1976). The present work was initiated to determine whether allozyme variation is concordant with the hypothesized relationships established by these previous studies and to ascertain whether enzyme data provide additional insights into these relationships. Additional questions addressed in this study include: (1) Are species as uniform at enzyme loci as they are in leaf flavonoid compounds and seed proteins? (2) Do enzyme data allow for distinguishing C. leptophyllum from other taxa? (3) Should C. incognitum be recognized as a species as suggested by Wahl (1952-53) or is it better treated as two biological entities? (4) Is C. hians as distinct from other taxa in its allozymes as it is in flavonoids and seed protein profiles? (5) Do allozymes provide additional insight into the