A faster rate of nuclear DNA evolution has recently been found for plants occupying warmer low latitudes relative to those in cooler high latitudes. That earlier study by our research group compared substitution rates within the variable internal transcribed spacer (ITS) region of the ribosomal gene complex amongst 45 congeneric species pairs, each member of which differed in their latitudinal distributions. To determine whether this rate differential might also occur within highly conserved DNA, we sequenced the 18S ribosomal gene in the same 45 pairs of plants. We found that the rate of evolution in 18S was 51% faster in the tropical plant species relative to their temperate sisters and that the substitution rate in 18S correlated positively with that in the more variable ITS. This result, with a gene coding for ribosomal structure, suggests that climatic influences on evolution extend to functionally important regions of the genome.

Circumscription and infrageneric classification of Kunzea is evaluated after phylogenetic analyses of nrDNA ITS and ETS sequences. Kunzea is monophyletic if the K. ericoides complex and the monotypic Angasomyrtus are included. The genus can be divided into western Australian, eastern Australian, and eastern Australian plus New Zealand clades. Angasomyrtus has greater affinity with the eastern Kunzea species, despite its western Australian endemic status. A new infrageneric classification is proposed, recognising four subgenera, with a further division into sections within two of these. A new combination in Kunzea is made for Angasomyrtus.

BACKGROUND AND AIMS:Crassula hunua and C. ruamahanga have been taxonomically controversial. Here their distinctiveness is assessed so that their taxonomic and conservation status can be clarified.METHODS:Populations of these two species were analysed using morphological, chromosomal and DNA sequence data.KEY RESULTS:It proved impossible to differentiate between these two species using 12 key morphological characters. Populations were found to be chromosomally variable with 11 different chromosome numbers ranging from 2n = 42 to 2n = 100. Meiotic behaviour and levels of pollen stainability were both variable. Phylogenetic analyses showed that differences exist in both nuclear and plastid DNA sequences between individual plants, sometimes from the same population.CONCLUSIONS:The results suggest that these plants are a species complex that has evolved through interspecific hybridization and polyploidy. Their high levels of chromosomal and DNA sequence variation present a problem for their conservation.

Because of its remoteness and mid-latitude position, New Zealand lacks access to the tropical climates that might have ensured straightforward survival for frost-sensitive species during glacial times. Nevertheless, the New Zealand lowland flora retains a substantial complement of plants sourced in the tropics. While there have been extinction pulses for elements of the frost-sensitive flora under glacial/stadial regimes, the surviving remnants have been able to recolonize large areas of habitat during successive warm climate periods. Refugia for such species in stadial New Zealand are likely to have been localized and ecologically suboptimal. To examine these relationships we have applied chloroplast DNA sequence data to the investigation of phylogeographical pattern for five endemic species of Metrosideros subg. Metrosideros, a wide-ranging group of mostly frost-sensitive woody plants in New Zealand. The results of this research verify the location of two generally mooted stadial refugia for the country and provide support for the existence of a third. A simple pattern of chloroplast haplotype diversity was recorded in extra-refugial areas, compared with a greater complexity in the vicinity of the identified refugia. This pattern was independently repeated in both main islands. The proposed refugia correspond to contemporary localities of high average winter temperatures. The sharing of chloroplast haplotypes between the different species of Metrosideros examined suggests that there has been a history of repeated hybridization and introgression for these plants, possibly initiated by periods of refugial confinement. (C) 2004 The Linnean Society of London.

AimTo examine patterns of hybridization and genotype mixing within the genus Coprosma J.R.Forst. & G.Forst. (Rubiaceae).LocationNew ZealandMethodsNucleotide 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.ResultsMixed 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.ConclusionsWe 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.

We have analysed the phylogenetic relationships of all known species in the genera Metrosideros and Carpolepis (Myrtaceae) from New Caledonia. Variation in nucleotide characters from the internally transcribed spacers of nuclear ribosomal DNA was used to construct parsimony and neighbour-joining phylogenies. These show that there is a large measure of congruence between the existing morphological taxonomy for those species and the relationships inferred from analyses of sequence variation. However, the DNA analyses suggest that Carpolepis may have only equal ranking to the infrageneric Metrosideros clades. The DNA analyses also nest M. tetrasticha among the species of subg. Metrosideros, as opposed to its present classification as a monotypic section (Neocaledonica) within subg. Mearnsia. On the basis of these findings, and of the observed differentiation shown in the analyses between the sectional clades Calyptropetala and Mearnsia of subg. Mearnsia, equivalent rankings may be appropriate for four infrageneric clades in Metrosideros. These four are currently classified as the genus Carpolepis (three species), and subg. Metrosideros (seven species), subg. Mearnsia sect. Mearnsia (five species) and subg. Mearnsia sect. Calyptropetala (five species) within Metrosideros.

Metrosideros bartlettii (Myrtaceae) is a distinctive and extremely rare tree, endemic to New Zealand, first discovered in 1975. Prior to this study, a total of 19 adult individuals of the species had been reported; these are located in three small forest remnants in the far north of the North Island of New Zealand. Here we describe a total of 31 adult M. bartlettii at the three sites, including 12 individuals newly discovered by us. We analyse the genetic diversity of the species, using microsatellites to examine the chloroplast genome and amplified fragment length polymorphisms (AFLPs) to monitor nuclear variation. The results clearly demonstrate that M. bartlettii is a unique species, distinct from its two closest relatives M. robusta and M. excelsa. Analysis of genetic diversity within the 31 remaining individuals of M. bartlettii showed an average heterozygosity (< H >) of 0.18 and a proportion of polymorphic genes (< P >) of 0.44. Population structure, as shown by 286 AFLP loci, varied between the three geographical sites; the site with fewest individuals, containing two trees, showed some separation from the populations at the other two locations. These two latter sites, by contrast, had highly overlapping AFLP population diversity profiles. The implications of these results for conservation of the species are discussed.