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Background and Aims: Miscanthus, a C4 perennial grass native to East Asia, is a promising biomass crop. Miscanthus sacchariflorus has a broad geographic range, is used to produce paper in China and is one of the parents (along with Miscanthus sinensis) of the important biomass species Miscanthus × giganteus. The largest study of M. sacchariflorus population genetics to date is reported here., Methods: Collections included 764 individuals across East Asia. Samples were genotyped with 34 605 single nucleotide polymorphisms (SNPs) derived from restriction site-associated DNA sequencing (RAD-seq) and ten plastid microsatellites, and were subjected to ploidy analysis by flow cytometry., Key Results: Six major genetic groups within M. sacchariflorus were identified using SNP data: three diploid groups, comprising Yangtze (M. sacchariflorus ssp. lutarioriparius), N China and Korea/NE China/Russia; and three tetraploid groups, comprising N China/Korea/Russia, S Japan and N Japan. Miscanthus sacchariflorus ssp. lutarioriparius was derived from the N China group, with a substantial bottleneck. Japanese and mainland tetraploids originated from independent polyploidization events. Hybrids between diploid M. sacchariflorus and M. sinensis were identified in Korea, but without introgression into either parent species. In contrast, tetraploid M. sacchariflorus in southern Japan and Korea exhibited substantial hybridization and introgression with local diploid M. sinensis., Conclusions: Genetic data indicated that the land now under the Yellow Sea was a centre of diversity for M. sacchariflorus during the last glacial maximum, followed by a series of migrations as the climate became warmer and wetter. Overall, M. sacchariflorus has greater genetic diversity than M. sinensis, suggesting that breeding and selection within M. sacchariflorus will be important for the development of improved M. × giganteus. Ornamental M. sacchariflorus genotypes in Europe and North America represent a very narrow portion of the species' genetic diversity, and thus do not well represent the species as a whole., (© The Author(s) 2018. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

This paper reviews recent new trends in population structure in the world and its major regions in order to access the determinants of those trends and explore issues regarding the recent and projected changes in the age structure of population and the relationships of those changes to social and economic development. In particular, the paper compares the change in age structure projected by the Population Division of the UN Secretariat in its most recent 3 series--namely, those completed in 1984, 1986, and 1988. By and large, the most recent UN assessment projects that a larger proportion of the world population will be aged 60 and over in 2000 and 2025 than was previously estimated. Those changes in projections can be observed for the world and for the more developed countries as a whole, and for the regions of Africa, Latin America, Northern America, East Asia, Europe, and Oceania. While the recommendations of the International Conference on Population called attention to the importance of changes in population structure, this paper recommends urgent government action in planning social programs for the aged because of the greater eminence of population aging in many settings. The case of Japan is used to illustrate the growing importance of increases in life expectancy as a determinant of age structure changes (in relation to fertility decline), a point that is reinforced through a cruder decomposition of UN estimates and projections for several European countries.