Karyotype evolution in conifers

Abstract

AbstractThe present study describes the published karyotypes of 338 conifer taxa comprising of 302 species belonging to 59 genera of conifers. The somatic chromosome numbers range from 2n=18 in Phyllocladus (Podocarpaceae) to 2n=66 in Sequoia sempervirens (Cupressaceae). Polyploidy is rare as out of 512 conifer taxa known cytologically 2.80 per cent are polyploid and 2.20 per cent have both diploid and polyploid cytotypes. Various families show uniform somatic numbers such as Pinaceae (2n=24), Araucariaceae (2n=26), Cupressaceae (2n=22) except for some cases of polyploid taxa, and Podocarpaceae (2n=18‐38) caused by centric fissions. In Pinaceae the genus Pinus has the most symmetrical karyotype and Larix has the maximum bimodality. The karyotype diversity in rest of the families has been discussed in the phylogenetic framework. This apparent uniformity of karyotypes is not reflected in diversity of fluorescent bands and rDNA loci. These additional markers have taxonomic relevance and also facilitate chromosome identification in a number of cases. This karyotype conservation is reflected in very weak interspecific crossing barriers with the hybrids showing normal meiosis, and also in the conservation of gene content and order.