The subgenus Ceratochloa of the genus Bromus includes a number of closely related allopolyploid forms or species that present a difficult taxonomic problem. The present work combines data concerning chromosome length, heterochromatin distribution and nuclear genome size of different 6x, 8x and 12x accessions in this subgenus. Special attention is paid to the karyotype structure and genomic constitution of duodecaploid plants recently found in South America. Hexaploid lineages possess six almost indistinguishable genomes and a nuclear DNA content between 12.72 pg and 15.10 pg (mean 1Cx value = 2.32 pg), whereas octoploid lineages contain the same six genomes (AABBCC) plus two that are characterized by longer chromosomes and a greater DNA content (1Cx = 4.47 pg). Two duodecaploid accessions found in South America resemble each other and apparently differ from the North American duodecaploid B. arizonicus as regards chromosome size and nuclear DNA content (40.00 and 40.50 pg vs. 27.59 pg). These observations suggest that the South American duodecaploids represent a separate evolutionary lineage of the B. subgenus Ceratochloa, unrecognized heretofore.

Variability in chromosome numbers of Plagiomnium affine from five populations in Poland was found with n = 6, 7, 12 and 18. Three populations showed intrapopulation karyological variability (n = 6, 12, 18), two others were karyologically uniform (n = 6). Additionally, mixoploidy was noted with haploid (n = 6, 7), haploid-diploid (n = 6, 12) and haploid-diploid-polyploid (n = 6, 12, 18) cells in one gametophytic apex.The haploid set consists of two chromosome types: metacentric and submetacentric. Their frequency in particular metaphase plates was different. Variation in karyotype was discovered within the population and among populations. Four types of karyotype were distinguished:The C-banding demonstrated one chromosome with a large telomeric heterochromatin block and one intercalary band. This chromosome was the fifth in the haploid complement according to chromosome length and was the only chromosome marker that is easy to identify in the C-banded karyotype. Centromeric bands were not observed.

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