Natural inter-subgeneric hybridization between Eucalyptus acmenoides Schauer and Eucalyptus cloeziana F. Muell (Myrtaceae) in southeast Queensland

Eucalyptus acmenoides Schauer (white mahogany) and E. cloeziana F. Muell (G ympie messmate) are largely allopatric but have several sympatric populatio ns across their range in eastern Queensland, Australia. In this study, veri fication of interspecific hybridization at the site of one such sympatric p opulation was carried out using morphological and molecular (nuclear and cy toplasmic) characters. Capsule morphology was intermediate in hybrids, part icularly with respect to the number of valves per capsule. Hybridization wa s found to occur in both directions with maternal inheritance of a taxon-sp ecific polymorphism in the inverted repeat of the J(LA) region of the chlor oplast genome. However, E. acmenoides acted as the maternal parent in all b ut one hybrid individual, possibly due to protandry of flowering. High leve ls of polymorphism in microsatellite loci existed between E. acmenoides and E. cloeziana in the hybrid zone. Formation of hybrids was most likely limi ted to F-1 mating and was restricted in both numbers and dispersal within t he hybrid zone. Current taxonomy places E. cloeziana and E. aemenoides into different subgenera, Idiogenes and Monocalyptus respectively. This is sign ificant as it is the only example of natural hybridization between subgener a within the Eucalyptus genus, suggesting that the taxonomic classification of E. acmenoides and E. cloeziana should be investigated further.