Karyotypes and chromosome evolution of polyploids of <i>Begonia</i> sect. <i>Platycentrum</i> (Begoniaceae) with chromosome numbers 2<i>n</i>=44, 60, and 66

We report the first chromosome counts for four species of Begonia sect. Platycentrum, three with 2n=44 and one with 2n=66, and reinvestigated the chromosome cytology of two species of the section with chromosome numbers of 2n=44 and 2n=60, respectively. The karyotypes of these six species are reported for the first time. Based on these karyotypes, species with 2n=44 and 2n=66 are shown to be tetraploids and hexaploid with x=11, respectively, whereas B. formosana (2n=60) is hypothesized to be an amphidiploid, likely originating from hybridization between a diploid with 2n=22 (i.e., B. longifolia or B. palmata) and a tetraploid with 2n=38, which are represented by four species endemic to Taiwan.