Taxonomy and biosystematics of the Chenopodium album aggregate.

This study concerns the evolutionary relationships of the taxa belonging to the C. album aggregate (C. album, C. probstii, C. giganteum and C. opulifolium, all 2n = 54; C. striatum, C. novopokrovskyanum, C. bushianum, C. berlandieri and C. quinoa, all 2n = 36; C. suecicum and C. ficifolium, both 2n = 18) from sect, Chenopodium. In addition, four other diploid species (C. vulvaria, C. murale, C. hybridum and C. polyspermum) from sect. Chenopodium and C. glaucum from sect. Pseudoblitum were studied. All the diploid species are distinguishable according to their leaf-shape and seed morphology. C. striatum and C. novopokrovskyanum (Old World tetraploids) have similar leaf- shape and seed morphology but differ from C. bushianum, C. berlandieri and C. quinoa (New World tetraploids). The latter three also possess similar leaf-shapes but C. bushianum and C. berlandieri have a different seed morphology from C. quinoa. Hexaploid taxa are differentiated into two groups (C. album, C. probstii and C. giganteum, and C. opulifolium) according to their leaf-shape, but seed morphology scarcely differs between them. Flavonoid chemistry showed that all diploid and New World tetraploid species studied have their own specific profiles. The Old World tetraploid and hexaploid taxa are very similar and combine characters of the two diploid species, C. suecicum and C. ficifolium. Isozyme studies showed all diploid species to have their own specific pattern. C. suecicum and C. ficifolium are the closest diploid species. The New World and Old World tetraploid species are differentiated from each other. At the hexaploid level C. album, C. probstii and C. giganteum are close to each other but C. opulifolium stands apart. This species shows more similarity to C. vulvaria than do the other hexaploid taxa. All alleles found in C. suecicum and C. ficifolium also occur in C. album, strongly implicating these diploids in the origin of the hexaploid. Based on the results of this study it can be concluded that an ancestral diploid gene pool evolved into C. suecicum in the north and C. ficifolium in the south. The Old World tetraploids originated from these two diploids or from taxa very similar to them. Backcrossing between diploids and tetraploids and chromosome doubling in the resulting triploid probably resulted in the hexaploid complex centred around C. album. Backcrossing between hexaploid taxa and closely related diploid species like C. vulvaria could have resulted in C. opulifolium.