Genetic relationships and inferred evolutionary divergence in the New Zealand taxa of Nothofagus — Results from isozyme analysis

Abstract

Genetic identity and standard genetic distance between the New Zealand taxa of Nothofagus, which are taxonomically distinguished at the subgeneric, specific, and varietal level, were derived from isozyme analysis of 22 gene loci. Average interpopulational genetic identities within and between the two recognised varieties of N. solandri are very similar and support their conspecific taxonomical status. Very high genetic identities, normally typical of conspecific plant populations, were also found between any two taxa of the 'fusca' group (subgenus Fuscospora), except for the pair N. truncata – N. solandri var. solandri (0.914). Average genetic identity between N. menziesii (subgenus Lophozonia) and all taxa of the 'fusca group is extremely low (0.060) and warrants the present subgeneric division. Inferred times of genetic divergence were compared with a small set of published data from amino acid sequencing of ribulose-1,s-bisphosphate carboxylase of some Nothofagus species. An ancient divergence of the two subgenera studied is implied, which reasonably matches late Cretaceous fossil records of the corresponding pollen types. A comparatively recent speciation, possibly during the late Pliocene to Pleistocene is assumed for the 'fusca' taxa.