Coexistence of apomictic tetraploids and sexual diploids drives the production of novel polyploid cytotypes with predominantly apomictic reproductive modes. The data suggest that processes governing cytotype diversity and mating system variation in Sorbus from Bosnia and Herzegovina are probably parallel to those in other diversity hotspots of this genus. The results represent a solid contribution to knowledge of the reproduction of Sorbus and will inform future investigations of the molecular and genetic mechanisms involved in triggering and regulating cytotype diversity and alteration of reproductive modes.

Genome size was assessed by flow cytometry in 33 species belonging to seven genera of the tribe Cardueae (Asteraceae), which can be grouped in three taxonomic complexes. 2C nuclear DNA content ranged from 1.49 to 16.98 pg, which is more than elevenfold variation. Genome size correlated well with some karyological traits. Nuclear DNA amount variations also have systematic and evolutionary implications and/or are linked to adaptations to ecological conditions.

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Seven Quercus species, four deciduous (Q. cerris, Q. petraea, Q. pubescens, andQ. robur) and three evergreen (Q. coccifera, Q. ilex, andQ. suber), were assessed for DNA content. Their genome sizes ranged from 1.88 to 2.00 pg/2C, namely an interspecific DNA content variation of 6%. In addition, the DNA content of several populations of Q. petraea andQ. robur with different geographical origins, French and Croatian, was estimated. DNA content did not vary among four populations of Q. robur, but did differ between two populations of Q. petraea, the French population having a higher 2C DNA value than the Croatian. The genome size of this French population showed important dispersion among 10 measured individuals. This was in accordance with subsequent cytogenetic data that revealed extra chromosomes in some individuals from this population. The percent GC varied little between the species; a GC content of 39.9% is established as typical for oak.Key words: Quercus, flow cytometry, genome size, GC percent, DNA content variations, extra chromosomes.

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