Eucalyptus subgenus Eucalyptus (Myrtaceae) trees are abundant sources of medicinal pinocembrin and related methylated flavanones

Abstract Plant-derived flavanones such as pinocembrin and related methylated forms are of interest for their potential medicinal use. Commercial sources of these compounds are limited, but some trees in genus Eucalyptus subgenus Eucalyptus (family Myrtaceae) show promise due to their high foliar flavanone content and growth rate, particularly when grown in coppice cultivation. As a first step to developing commercial Eucalyptus plantations for flavanone production, this research aimed to identify high-yielding species. Foliar flavanones were quantified in 41 species and subspecies from three major sections within the subgenus. Pinocembrin concentrations were highest in two subspecies of E. preissiana with notably high levels of 15 and 18 mg g –1 dry weight (DW). The highest concentrations of 7- O -methylpinocembrin (12 mg g –1 DW ) and 5,7- O -dimethylpinocembrin (20 mg g –1 DW ) were found in E. croajingolensis and E. oreades , respectively. In addition, two C -methyl flavanones were identified in Eucalyptus for the first time: 6- C -methylpinocembrin (7 mg g –1 DW ) in E. megacarpa and 6,8- C -dimethylpinocembrin (6 mg g –1 DW ) in E. agglomerata . In general, flavanone profiles for closely related eucalypts such as subspecies were very similar. Moreover, species fit into three distinct categories - those with high concentrations of relatively pure non-methylated pinocembrin, those with highly abundant O -methyl flavanones, or those with abundant C -methyl flavanones. Saplings of two selected species grown in a trial plot largely reflected adult tree flavanone profiles, albeit at lower levels attributed to ontogenetic effects. In conclusion, we have shown that many species of Eucalyptus are abundant sources of promising medicinal flavanones. This work will enable selection of high-yielding species and genotypes for growth-rate assessment trials and the future establishment of commercial plantations.