Polyploidy, particularly allopolyploidy resulting from interspecific hybridization followed by chromosome duplication, plays a key role in plant diversification and ecological success. Chenopodium album s. str. is one of the world's most widespread and morphologically variable weeds, yet the timing and mechanism of its origin as an allohexaploid (2n = 6x = 54) remained unresolved. Using RADseq data, this study investigated the origin of 'BBCCDD' allohexaploid C. album s. str. and closely related hexaploid taxa by analyzing their relationship to putative diploid progenitors with the 'BB' genome (C. ficifolium, C. suecicum, C. ucrainicum) and tetraploid species with the 'CCDD' subgenomic combination (C. betaceum, C. glaucophyllum, C. novopokrovskyanum, C. striatiforme). The genomic sequences were mapped to the chromosome-scale reference genome of C. formosanum, a closely related allohexaploid. Results reveal that C. album s. str. does not genetically align with contemporary diploid or tetraploid taxa, suggesting its origin from extinct ancestors rather than ongoing hybridization. Both its 'BB' and 'CCDD' subgenomes show higher or comparable number of genetic lineages, respectively, than its extant di- and tetraploid relatives, implying conservation of ancestral variation in the allohexaploid. Furthermore, 16 distinct subgenomic combinations were identified within C. album s. str., confirming its polytopic and repeated origin across geographic regions. This explains the remarkable morphological and ecological plasticity observed across its range. This research underscores C. album s. str. as an ancient, stabilized, and globally invasive polyploid, shaped by multiple hybridization events and fixed heterozygosity, offering parallels with other polyploid species such as Triticum/Aegilops complex.
Mandák et al. (2025) studied this question.
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