Genome Size in Angiosperms: Temperate Versus Tropical Species

The presence of genome size differences between tropical and temperate plants was sought in a literature survey including 368 tropical and 524 temperate herbs. The mean and total chromosome lengths of pairs of chromosome complements of tropical plants are smaller than those properties of temperate plants. The mean length of chromosomes of tropical plants is 3.1 μ compared to 5.6 μ for temperate plants. The total chromosome length of the former assemblage is 61.3 μ versus 105.9 μ for the latter assemblage. The mean diploid number of the plants from each geographical region is near 19. Thus differences in length of chromosome complements are not attributable to numbers of chromosomes. Therefore, in general, genome size is larger in temperate herbs than in tropical ones. A comparison of 4C-DNA contents of species as presented in the literature showed that the genome sizes of temperate species is more than twice that of tropical species. The temperate-tropical differential present in angiosperms as a whole is not consistently present within families. In the Gramineae the mean chromosome length of temperate species is more than three times greater than that in tropical species; a difference of similar magnitude is present for total chromosome length. However, in other large cosmopolitan families such as the Leguminosae and Compositae no significant differences were present. Although no consistent pattern is evident within families, on the average, families indigenous to tropical and subtropical regions have substantially smaller genomes than those of temperate regions. Thus replacement of species in space in accordance with their family affiliation seems to be responsible for the general difference between temperate and tropical species.