The genus Ceiba Mill. belongs to the subfamily Bombacoideae (Malvaceae), a paleopolyploid lineage characterized by numerous small chromosomes, which has frequently been reported to have variable intra-and interspecific chromosome numbers. The genus is of Miocene origin, representing a suitable model for studying the relationships between chromosome variability and paleopolyploidy. A comparative cytogenetic analysis of five Ceiba species was undertaken to determine their karyotype variability. New chromosome number counts, chromosome morphological observations, CMA/DAPI double staining, and in situ hybridization (FISH) with 5S and 45S rDNA were performed for five Ceiba species, which represent three out of five main lineages of the genus. Karyotypic data were discussed in the light of molecular phylogenies available for the group. All species showed 2n = 86 and similar karyotypes, composed predominantly of metacentric chromosomes. Two pairs of CMA ? /DAPIbands were located on the short arms of the metacentric chromosomes. The CMA ? bands colocated with 45S rDNA sites, while the 5S rDNA sites were situated in the interstitial regions of other chromosome pairs. Contrary to the intra-and interspecific chromosome number diversity reported for Ceiba species in the literature, our findings suggest chromosome number stability in four of the five lineages within the genus for which data are available. Moreover, our data suggest that karyotypes are evolutionary conserved in the three lineages for which we generated new karyotypic data. Our data, as well as recent cytogenetic reviews of other Bombacoideae genera, indicate numerical stability for these taxa suggesting that counting errors, especially in earlier research, may have overestimated karyotype variability. Chromosome count errors can be attributed to technical difficulties associated with high chromosome numbers, and/or the reduced size of Bombacoideae chromosomes.

Stylosanthes (Papilionoideae, Leguminosae) is a predominantly Neotropical genus with~48 species that include worldwide important forage species. This study presents the chromosome number and morphology of eight species of the genus Stylosanthes (S. acuminata, S. gracilis, S. grandifolia, S. guianensis, S. hippocampoides, S. pilosa, S. macrocephala, and S. ruellioides). In addition, staining with CMA and DAPI, in situ hybridization with 5S and 35S rDNA probes, and estimation of DNA content were performed. The interpretation of Stylosanthes chromosome diversification was anchored by a comparison with the sister genus Arachis and a dated molecular phylogeny based on nuclear and plastid loci. Stylosanthes species showed 2n = 20, with low cytomolecular diversification regarding 5S rDNA, 35S rDNA, and genome size. Arachis has a more ancient diversification (~7 Mya in the Pliocene) than the relatively recent Stylosanthes (~2 Mya in the Pleistocene), and it seems more diverse than its sister lineage. Our data support the idea that the cytomolecular stability of Stylosanthes in relation to Arachis could be a result of its recent origin. The recent diversification of Stylosanthes could also be related to the low morphological differentiation among species, and to the recurrent formation of allopolyploid complexes.