Genetic relationships among larch species based on analysis of restriction fragment variation for chloroplast DNA

The genetic relationships among eight species and three varieties within the genus Larix were studied by analysing restriction fragment length polymorphism in chloroplast DNA (cpDNA). Six restriction enzymes and 11 predominantly nonoverlapping probes from Pinus contorta Dougl. ex Loud. were employed. No variation in cpDNA was detected within taxa, and mean levels of nucleotide divergence (d) among species were low. Six taxa were not resolved by the analysis, and the maximum d value recorded was 0.0096. Genetic distance data and neighbor joining were used to construct a tree of genetic relatedness among taxa, which resolved three groups. Larix griffithiana Carr. was genetically distinct from all other taxa. A second group comprised Larix sibirica Ledeb. from Eurasia and two North American species, Larix laricina (Du Roi) K Koch. and Larix occidentalis (Nutt.). The third group consisted of the Chinese and Japanese taxa Larix gmelinii (Rupr.) Rupr. ex Kuzen., Larix potaninii Batal., and Larix kaempferi (Lamb.) Carr. together with European larch, Larix decidua Mill. These groupings do not correspond to traditional patterns of classification within the genus, which are based primarily on features of the female cone. The results from the cpDNA analysis are interpreted in the context of other information about the evolutionary history of the genus.