No abstract

No abstract

Aim We hypothesised that during the Holocene, the distributions of species such as crop weeds have been significantly influenced by human activity. We aimed to (a) identify the main centres of diversity of the Chenopodium album agg. species and (b) test if these species colonised Europe from western Asia, most likely due to the westward expansion of agriculture in the Neolithic period. Location Eurasia. Taxon Chenopodium album aggregate (Amaranthaceae). Methods Three cpDNA regions were sequenced in 904 individuals, from 26 species of the C. album aggregate. A dated phylogeny was inferred and this was used to establish relationships among the haplotypes and to estimate their divergence times. The group's main centres of diversity were inferred by comparing species and haplotype richness between Europe, the Mediterranean, western Asia, central Asia and Siberia. Results The most haplotype‐diverse area for the entire C. album aggregate is central Asia. Interestingly, Europe is poor in terms of haplotype diversity, showing the same level of diversity as the western Asian region. The pairwise genetic differentiation between Europe, the Mediterranean and western Asia is lower than between any of these regions and either central Asia or Siberia. This points to the origin of the European Chenopodium species pool as being in western Asia. In some phylogenetically‐defined clades, species could not be distinguished based on cpDNA haplotypes due to a high level of haplotype sharing. However, in others, the haplotype variation follows the species boundaries. Main conclusions Using the C. album agg. species as a model, we show the importance of central Asia as one of the main centres of diversity for weedy species. However, the group's colonisation of Europe had its origins in western Asia, highlighting the importance of human‐mediated dispersal of ruderal and weed plant species accompanying the westward spread of agriculture in the Neolithic period.

The study of variation in nuclear genome size, especially when combined with common garden experiments, significantly contributes to disentangling interspecies relationships within taxonomically complicated plant groups. The Chenopodium album aggregate is among the morphologically most variable groups and consists of many weakly differentiated cosmopolitan entities. We analysed nuclear genome size variation in diploid and polyploid species of the aggregate from Iran using flow cytometry of 282 accessions from 88 populations of 7 species. To this end, we also determined chromosome numbers and performed a morphometric study to reveal the extent of intraspecific morphological variation. We found that Iranian species are exclusively diploid (C. vulvaria), tetraploid (C. novopokrovskyanum, C. strictum, C. sosnowskyi and C. chaldoranicum) or hexaploid (C. album subsp. album, C. album subsp. iranicum and C. opulifolium). Six homogeneous relative genome size groups were distinguished among the species studied. Our morphometric study surprisingly revealed that under similar ecological conditions Chenopodium species are morphologically stable and well distinguishable, exhibited very little morphological variation. Hence, immense variation in leaf shapes, branching and inflorescence organization seen in the field has not been repeated under greenhouse conditions. The only exception was C. album s. str. which exhibited numerous morphotypes, covering the variation of remaining species.