Nuclear DNA Amounts in Gymnosperms

A survey of genome size variation in 117 gymnosperms has found that the systematic coverage of the measurements is uneven, some families have been well sampled but others have not. There is a 144-fold variation in genome size within the group; the largest genome being that of Pinus lambertiana with 63'5 pg DNA/2C nucleus and the smallest, 1296 pg DNA/2C nucleus in Metasequoia glyptostroboides. The different methods that have been used to measure genome size in gymnosperms, the choice of standards, and problems associated with the different methods are reviewed. The conflicting reports of intraspecific variation in genome size in gymnosperm species are problematic. Some appear real whereas others can be attributed to problems associated with methodology. Some studies of species show considerable uniformity of genome size over a wide geographical range whereas others find high levels of variation which may, in some cases, be correlated with geographical parameters. Possible correlations between genome size and adaptive features of gymnosperms are examined and a number of correlations are reported between genome size and growth-related parameters.