**5. Cytological investigations and genome size comparisons**

*Begonia* exhibit a highly dynamic genome, with large variation in chromosome number, genome size and mean chromosome size as well as divergent chromosome structure, even between closely related species (Dewitte et al., 2009a). Traditionally, investigations at the chromosome level have been hindered by the small size of *Begonia* chromosomes, the difficulty in visualising centromeres, and few reliable karyograms. However, recent investigations using horticultural hybrids between divergent species, as well as cytological studies in the context of phylogenetic relationships, have greatly improved our understanding of this cytologically interesting genus.
