This expanded survey of ITS sequences represents the largest analysis of molecular data ever attempted on Eucalyptus. Sequences of the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA were included in an analysis of 90 species of Eucalyptus s.s. and 28 species representing eight other genera (Allosyncarpia, Angophora, Arillastrum, Corymbia, Eucalyptopsis, Stockwellia, Lophostemon and Metrosideros). The results of the study indicate that Angophora and Corymbia form a well-supported clade that is highly differentiated from Eucalyptus s.s. Corymbia species are divided between two clades, one of which may be the sister to Angophora. Allosyncarpia, Arillastrum, Eucalyptopsis and ‘Stockwellia’ are also highly differentiated from Eucalyptus s.s. If the genus Eucalyptus is to be expanded to include Angophora and Corymbia(sensu Brooker 2000), ITS data suggest that Allosyncarpia, Eucalyptopsis, ‘Stockwellia’ and potentially Arillastrum should also be included in Eucalyptus s.l. The ITS data suggest that subg. Symphyomyrtus is paraphyletic and that subg. Minutifructus should be included within it. Within subg.Symphyomyrtus, only sect. Maidenaria appears to be monophyletic. Sections Adnataria and Dumaria are probably monophyletic; sections Exsertaria and Latoangulatae are very close and probably should be combined in a single section. Section Bisectae is polyphyletic and is divided into two distinct lineages. The phylogenetic groups depicted by ITS data are consistent with the frequency of natural inter-specific hybridisations as well as data from controlled crosses within subgenus Symphyomyrtus. The ITS data illustrate that subg. Idiogenes and western Australian monocalypts are early evolutionary lines relative to E. diversifolia, E. rubiginosa (monotypic subg. Primitiva) and the eastern monocalypts and that subg. Primitiva should be sunk into subg. Eucalyptus. Subgenus Eudesmia may be monophyletic, grouping with subgenera Idiogenes and Eucalyptus. Further work is required to confirm the phylogenetic positions of the monotypic subgenera Alveolata, Cruciformes, Acerosae and Cuboidea.

Leaves and samples of recent wood of Eucalyptus species were collected along a rainfall gradient parallel to the coast of Western Australia between Perth in the north and Walpole in the south and along a southwest to northeast transect from Walpole in southwestern Australia, to near Mount Olga in central Australia. The collection included 65 species of Eucalyptus sampled at 73 sites and many of the species were collected at several sites along the rainfall gradient. Specific leaf area (SLA) and isotopic ratio of 13C to 12C (delta 13C) of leaves that grew in 2002, and tree ring growth and delta 13C of individual cell layers of the wood were measured. Rainfall data were obtained from the Australian Bureau of Meteorology for 29 locations that represented one or a few closely located collection sites. Site-averaged data and species-specific values of delta 13C decreased with decreasing annual rainfall between 1200 and 300 mm at a rate of 1.63 per thousand per 1000 mm decrease in rainfall. Responses became variable in the low rainfall region (< 300 mm), with some species showing decreasing delta 13C with rainfall, whereas delta 13C increased or remained constant in other species. The range of delta 13C values in the low rainfall region was as large as the range observed at sites receiving > 300 mm of annual rainfall. Specific leaf area varied between 2 and 6 m2 kg(-1) and tended to increase with decreasing annual rainfall in some species, but not all, whereas delta 13C decreased with SLA. The relationship between delta 13C and SLA was highly species and soil-type specific. Leaf-area-based nitrogen (N) content varied between 2 and almost 6 g m(-2) and decreased with rainfall. Thus, thicker leaves were associated with higher N content and this compensated for the effect of drought on delta 13C. Nitrogen content was also related to soil type and species identity. Based on a linear mixed model, statistical analysis of the whole data set showed that 27% of the variation in delta 13C was associated with changes in SLA, 16% with soil type and only 1% with rainfall. Additionally, 21% was associated with species identity. For a subset of sites with > 300 mm rainfall, 43% of the variation was explained by SLA, 13% by soil type and only 3% by rainfall. The species effect decreased to 9% because there were fewer species in the subset of sites. The small effect of rainfall on delta 13C was further supported by a path analysis that yielded a standardized path coefficient of 0.38 for the effect of rainfall on SLA and -0.50 for the effect of SLA on delta 13C, but an insignificantly low standardized path coefficient of -0.05 for the direct effect of rainfall on delta 13C. Thus, in contrast to our hypothesis that delta 13C decreases with rainfall independent of soil type and species, we detected no statistically significant relationship between rainfall and delta 13C in leaves of trees growing at sites receiving < 300 mm of rainfall annually. Rainfall affected delta 13C indirectly through soil type (a surrogate for water-holding capaci...

A set of over 8000 Diversity Arrays Technology (DArT) markers was tested for its utility in high-resolution population and phylogenetic studies across a range of Eucalyptus taxa.Small-scale population studies of E. camaldulensis, E. cladocalyx, E. globulus, E. grandis, E. nitens, E. pilularis and E. urophylla demonstrated the potential of genome-wide genotyping with DArT markers to differentiate species, to identify interspecific hybrids and to resolve biogeographic disjunctions within species. The population genetic studies resolved geographically partitioned clusters in E. camaldulensis, E. cladocalyx, E. globulus and E. urophylla that were congruent with previous molecular studies. A phylogenetic study of 94 eucalypt species provided results that were largely congruent with traditional taxonomy and ITS-based phylogenies, but provided more resolution within major clades than had been obtained previously. Ascertainment bias (the bias introduced in a phylogeny from using markers developed in a small sample of the taxa that are being studied) was not detected.DArT offers an unprecedented level of resolution for population genetic, phylogenetic and evolutionary studies across the full range of Eucalyptus species.

A survey of regenerative strategies in the eucalypts, including lignotuber development, was undertaken by extensive field observations, seedling trials and trials of cultivated individuals over a 12-year period. Four broad regenerative strategies were identified, viz. obligate seeders, lignotuber sprouters, stem sprouters and combination sprouters. These four regenerative strategies are based on the ability to develop a lignotuber and the regeneration strategy after whole-crown destruction. These regenerative strategies do not wholly correspond to the tree, mallee, mallet, marlock and shrub habit categories commonly applied to eucalypts. The obligate seeders include many more terminal taxa than have been previously documented as mallet taxa, with 78 western obligate seeders (the ‘true’ mallets) and nine eastern obligate seeders listed herein. Obligate seeders do not possess a lignotuber and are killed by crown-destructive events, and as such are relatively short-lived in most natural environments. A further 16 taxa are also known to be non-lignotuberous, but these are capable of producing epicormic regrowth from the trunk following crown destruction and are defined as stem sprouters. The remaining two regenerative strategies include taxa that are both lignotuberous and able to regenerate vegetatively following disturbance events. The persistent and conjecturous mallet–marlock–moort distinction is rejected, this study showing it to be dependent on stand density. Data presented indicate no significant difference in germination time or maturation time between western obligate-seeder taxa and closely related sprouter taxa. The conservation status of obligate-seeder taxa is discussed. Nomenclatural issues regarding the taxonomic distinction between obligate-seeder and resprouter sister taxa are discussed. A census of regenerative strategies for all recognised eucalypt taxa is included as an accessory publication on the web.

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