Polyploidization, or genome duplication, has played a critical role in the diversification of animals, fungi and plants. Little is known about the population structure and multiple origins of polyploid species because of the difficulty in identifying multiple homeologous nuclear genes. The allotetraploid species Arabidopsis kamchatica is closely related to the model species Arabidopsis thaliana and is distributed in a broader climatic niche than its parental species. Here, we performed direct sequencing of homeologous pairs of the low-copy nuclear genes WER and CHS by designing homeolog-specific primers, and obtained also chloroplast and ribosomal internal transcribed spacer sequences. Phylogenetic analysis showed that 50 individuals covering the distribution range including North America are allopolyploids derived from Arabidopsis lyrata and Arabidopsis halleri. Three major clusters within A. kamchatica were detected using Bayesian clustering. One cluster has widespread distribution. The other two are restricted to the southern part of the distribution range including Japan, where the parent A. lyrata is not currently distributed. This suggests that the mountains in Central Honshu and surrounding areas in Japan served as refugia during glacial-interglacial cycles and retained this diversity. We also found that multiple haplotypes of nuclear and chloroplast sequences of A. kamchatica are identical to those of their parental species. This indicates that multiple diploid individuals contributed to the origin of A. kamchatica. The haplotypes of low-copy nuclear genes in Japan suggest independent polyploidization events rather than introgression. Our findings suggest that self-compatibility and gene silencing occurred independently in different origins.

Karyotype analyses were carried out on 73taxa of Brachyscm and Btaxa of its allied genera, Australian Astereae. Statistical tests regarding correlations between changes in chromosome number, total chromosome length, mean chromosome length, karyotypic asymmetry and chromosome length heterogeneity and changes in habd were performed based on the matK molecular phylogenetic tree. The reductions in chromosome number and total chromosome length, and the increases in mean chromosome length, chromosome length heterogeneity and karyotypic asymmetry were found to be correlated with the change in habit from perennial to annual. A reduction in total chromosome length is favored to shorten the mitotic cell cycle and to produce smaller cells conducive to more rapid development of smaller annuals under the time-limited environment. Stepwise dysploidal reductions in chromosome number were achieved through the translocation of large chromosome segments onto other chromosomes, followed by the loss of a centromere, resulting in one fewer linkage group and one fewer haploid chromosome. The correlations between the dysploidal reduction in chromosome number and the increases in mean chromosome length, length heterogeneity and asymmetry in karyotype can be attributed to this mode of chromosomal change. These changes occurred independently in several different lineages in Brachyscom.

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Chromosome number determinations from 152 collections representing 42 genera and 106 species of the Australian Gnaphalieae and Plucheeae are reported. The chromosome numbers of 75 of these species have not been previously counted or differ from those previously reported for species. Chromosome numbers have been documented for the first time for 14 genera: Argyroglottis (n = 12), Cephalosorus (2n = 24), Decazesia (n = 14), Dielitzia (2n = 26), Eriochlamys (n = 14), Erymophyllum (n = 11 and 14), Gilruthia (n = 13), Leucochrysum (n = 9), Myriocephalus s. str. (n = 14, 2n = 24), Polycalymma s. str. (n = 14), Pterocaulon (n = 10), Pterochaeta (n = 12), Quinetia (2n – 24) and Sondottia (2n = 6). Remaining counts augment and agree with previously reported determinations. Some problems with generic delimitation and interpretation of chromosome data are outlined. There is an array of karyotypes within the Australian Gnaphalieae and dysploidy is widespread. Polyploidy has also played an important role in the evolution of some taxa. Evidence suggests that the base number for Australian Gnaphalieae is x = 14. This may be the base number for the entire tribe.