Cytological Study of Begonia Sect. Baryandra (Begoniaceae)

Begonia sect. Baryandra is distributed mainly in the Philippines with a few species in Borneo and New Guinea. Previous chromosome information of sect. Baryandra has restricted to ca. 16 species and their karyotypes have never been investigated. Here we report the cytological investigations of 26 species of sect. Baryandra, including five karyotype analyses that are the first report in sect. Baryandra, 24 species were reported cytologically for the first time, and two species were re-examined. Incorporating previous and present studies, chromosome numbers of 40 of the 78 species in sect. Baryandra are now available. Except for some intraspecific variant counts of 2n = 26 and 44, and a tetraploid number of 2n = 56, 39 species have the chromosome number of either 2n=28 or 30. The karyotypic formula of the three investigated species is uniform as 2n = 28 = 10m+ 18sm(st), and two as 2n = 30=8m+22sm(st). Based on molecular phylogenetic relationships, ancestral state reconstruction suggests that 2n=30 is the most likely ancestral chromosome number of sect. Baryandra, with 2n=28 a derived number. Based on our and previous studies, the chromosome evolution in Begonia sect. Baryandra is discussed.