Polyploidy is a key factor in the evolution of higher plants and plays an important role in the variation of plant genomes, leading to speciation in some cases. During polyploidisation, different balancing processes take place at the genomic level that can promote variation in nuclear DNA content. We estimated genome size using flow cytometry in 84 populations of 67 Artemisia species and one population of Crossostephium chinense. A total of 73 sequences of nrDNA ITS and 3'-ETS were newly generated and analysed, together with previously published sequences, to address the evolution of genome size in a phylogenetic framework. Differences in 2C values were detected among some lineages, as well as an increase of genome size heterogeneity in subgenera whose phylogenetic relationships are still unclear. We confirmed that the increase in 2C values in Artemisia polyploids was not proportional to ploidy level, but 1Cx genome size tended to decrease significantly when high ploidy levels were reached. The results lead us to hypothesise that genome size in polyploids tends to a maximum as it follows saturation behaviour, in agreement with the Michaelis-Menten model. We tested different arithmetic functions with our dataset that corroborated a non-linear relationship of genome size increase in polyploids, allowing us to suggest a theoretical upper limit for the DNA content of this genus.

Different wild Mediterranean populations of Artemisia arborescens from diverse locations, representing its geographical distribution, as well as some of its well-known cultivars and some specimens cultivated as omamentals in gardens, streets, roads and nurseries, were analysed for genome size estimation. Other closely related species endemic to Macaronesia, A. canariensis, A. argentea and A. gorgonum, were also measured, and their nuclear DNA amount has been related to the biogeography of this group of species. Additionally, five populations of the closely related A. absinthium were analysed to establish comparisons. Measurements, acquired by flow cytometry, ranged from 8.29 pg to 11.61 pg for 2C values. Statistically significant differences of nuclear DNA amounts with respect to factors such as insularity or domestication have been detected. However, a quite low intraspecific genome size variation has been detected in these species. Furthermore, the study also addressed the possible hybrid origins, and possible misidentifications of some of the supposed cultivars ofA. arborescens..