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The red mahogany group (Eucalyptus ser. Annulares Blakely) includes some of the most important commercial species (i.e. Eucalyptus urophylla S.T.Blake) worldwide for forestry in the subtropics and tropics. However, the taxonomic status of some species in this group is unclear and the relationship among and genetic structuring within some species is unresolved. The present study examined genetic variation at 13 microsatellite loci in E. pellita F.Muell., E. resinifera Smith and E. scias L.Johnson & K.Hill. Despite close geographical proximity and natural hybridisation in northern Queensland, E. resinifera and E. pellita remain genetically distinct as taxa. Within E. pellita, two genetic groups were clearly resolved, one from New Guinea and one from Queensland (Cape York Peninsula populations were not sampled). Geographic structuring was also evident in E. resinifera, with northern Queensland populations separating from those from Fraser Island southwards. Ecological factors and species disjunctions were implicated in the genetic substructuring of these two taxa because patterns of geographic variation aligned with biogeographical regions. E. scias was indistinguishable from southern E. resinifera and its three subspecies could not be resolved.

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The frequency of polyploid trees in 10 populations of the predominantly diploid species Acacia dealbata subsp. dealbata Link in south-eastern Tasmania was determined using flow cytometry. At seven of the sites, all trees were diploid. At two sites, single triploid genets were found and, at a third, two tetraploids. Microsatellite markers were used to confirm that triploid trees distributed over an area of at least 930 m2 at the major study site were all ramets of a single genet. Three diploid clones were also confirmed at this site. The 16-grain polyads from the triploid genet were significantly larger than those from diploids, but only the diploid pollen showed any viability in vitro. At three months the green pods on diploids averaged 36 mm and contained four developing seeds per pod. Pods on the triploid were only 13 mm long, with no developing seeds. In spite of maturing pods, two of the diploids did not yield full seed, whereas two other diploids averaged only 0.1 seeds per pod. Seeds were not produced on triploid trees. The low reproductive output is discussed with reference to the breeding system and the impact of clonality on effective cross-pollination.

No abstract