Aim The majority of Hawaii's plants are derived from the south and west of the Paci®c rim, suggesting that at least some of the founders have crossed the climatic discontinuity at the equator. However, the pathways of these dispersal events are not well understood. We sought to elucidate such a pathway for the plant genus Metrosideros Banks ex Gaertn., which appears to have colonized Hawaii from New Zealand.Location We have previously analysed the internal transcribed spacer (ITS) sequence of nrDNA for thirty-six taxa of Metrosideros subgenus Metrosideros distributed across Melanesia and Polynesia. Further we collected two taxa from the Austral and Marquesas Islands.Methods Phylogenetic analysis was undertaken using both the ITS and external transcribed spacer (ETS) regions of nrDNA for twenty-three taxa from Polynesia and East Melanesia. ResultsThe increased resolution achieved by combining ETS data with that of ITS allowed discrimination of two subclades in eastern Oceania. One subclade groups all the Hawaiian taxa together with M. collina (J. R. & G. Forst.) A. Gray from the Marquesas Islands.Main conclusions From an origin in New Zealand, the woody angiosperm Metrosideros is likely to have crossed the equator to Hawaii using a staging point in the remote Marquesas Islands. Colonization of Hawaii by the wind-borne seed of these plants has been achieved against the¯ow of the prevailing Trade winds north of the equator. A possible climatic mechanism for this dispersal is described.

Aim To examine patterns of hybridization and genotype mixing within the genus Coprosma J.R.Forst. & G.Forst. (Rubiaceae). Location New Zealand Methods Nucleotide sequence was determined for the internal transcribed spacer (ITS) and external transcribed spacer (ETS) regions of nuclear ribosomal DNA for fifty individuals from thirty‐six taxa within the New Zealand component of the genus Coprosma. Results Mixed sequences were found to be widespread in Coprosma. Direct sequencing of ITS polymerase chain reaction (PCR) products from seven polyploid taxa showed evidence of sequence mixtures. Cloning and sequencing of individual PCR products from two polyploids confirmed the presence of multiple templates, one of which corresponded to that of a diploid. Intra‐individual heterogeneity was also seen in a hybrid diploid taxon, with the mixed nucleotides corresponding to those of the parental lineages. Finally the ITS sequences of twenty‐two diploid taxa showed that eleven contained intra‐individual heterogeneity. Conclusions We conclude that the widespread occurrence of sequence mixtures in Coprosma results from of frequent hybridization. We also conclude that concerted evolution of the ITS and ETS regions is depressed. We propose that these characteristics evolved as a mechanism to maintain high levels of heterogeneity and suggest that this is adaptive for Coprosma in climatically unstable and physically complex New Zealand landscapes. These landscapes have been subjected to repeated oscillations between stadial and interstadial environments during the Pleistocene.

A molecular phylogenetic analysis of New Zealand Coprosma using the internal transcribed spacer (ITS) and external transcribed spacer (ETS) regions of nrDNA discovered a consistent ITS sequence difference of eight base pairs between multiple samples of the widespread Coprosma obconica subsp. obconica and samples of the North Cape ultramafic endemic subsp. distantia. These DNA sequence results, coupled with those differences already described for both subspecies and the subsequent discovery of significant differences in the pyrene morphology of both subspecies, indicate that C. obconica subsp. distantia should be elevated to species rank. The necessary combination at the rank of species is made in this paper.