Fluorochrome-banded karyotypes of eight populations belonging to five taxa of the genus Artemisia from different European origins are presented. The most common basic number x = 9 is found in six populations of two diploid and two tetraploid species, whereas two populations of one diploid species have the less frequent basic number x = 8. The data on chromosome morphology and fluorochrome banding lead to some karyosystematic and evolutionary considerations, among others the postulation of descendent dysploidy to explain the occurrence of the two basic numbers in the genus. Key words: Asteraceae, Anthemideae, Artemisia, karyotypes, fluorochrome banding, cytotaxonomy, evolution.

In this study we showed that constitutive heterochromatin, GC-rich DNA and rDNA are implicated in chromosomal rearrangements during the basic chromosome number changing (dysploidy) in Reichardia genus. This small Mediterranean genus comprises 8–10 species and presents three basic chromosome numbers (x = 9, 8 and 7). To assess genome evolution and differentiation processes, studies were conducted in a dysploid series of six species: R. dichotoma, R. macrophylla and R. albanica (2n = 18), R. tingitana and R. gaditana (2n = 16), and R. picroides (2n = 14). The molecular phylogeny reconstruction comprised three additional species (R. crystallina and R. ligulata, 2n = 16 and R. intermedia, 2n = 14). Our results indicate that the way of dysploidy is descending. During this process, a positive correlation was observed between chromosome number and genome size, rDNA loci number and pollen size, although only the correlation between chromosome number and genome size is still recovered significant once considering the phylogenetic effect. Fluorescent in situ hybridisation also evidenced changes in number, position and organisation of two rDNA families (35S and 5S), including the reduction of loci number and, consequently, reduction in the number of secondary constrictions and nuclear organising regions from three to one per diploid genome. The potential mechanisms of chromosomal and genome evolution, strongly implicating heterochromatin, are proposed and discussed, with particular consideration for Reichardia genus.

Polyploidy and natural hybridization are considered as two major evolutionary processes involved in plant speciation and diversification. In conifers, natural hybridization has been noticed to be more frequent than polyploidy. Nevertheless, a few cases of polyploidy have been reported in the genus Juniperus. In this genus, a new variety Juniperus sabina var. balkanensis has been postulated to have arisen from an ancient hybridization between the tetraploid species Juniperus thurifera and the diploid species Juniperus sabina var. sabina. The genome size variation and the ploidy level of two J. sabina taxa were estimated by flow cytometry in a panel of 29 populations. All 13 populations of J. sabina var. sabina were diploid, with genome sizes ranging from 22.09 to 25.03 pg/2C, while the 16 populations of J. sabina var. balkanensis were tetraploid, with genome sizes ranging from 41.99 pg to 51.33 pg/2C. These findings open new venues towards the discovering of the polyploidization pathway of J. sabina var. balkanensis and to understand historical and ecological factors that explain its current geographical distribution.