Interspecific Hybridization withinEucalyptus(Myrtaceae): SubgenusSymphyomyrtus, SectionsBisectaeandAdnataria

The potential for interspecific hybridization within the genusEucalyptuswas investigated through controlled pollination and measurement of seedling leaf morphology.Eucalyptus gilliiandE. socialis(subgen.Symphyomyrtussect.Bisectaeser.Subulatae) were used as the female parents, and pollen was sourced from 16Eucalyptusspecies from a number of series within sectionsBisectaeandAdnataria(subgen.Symphyomyrtus). Thirty‐four out of 36 crosses produced seeds; however, the percentage of seeds produced per flower pollinated varied considerably between crosses, as did germination percentage and seedling survival. At 3 mo of age, all surviving seedlings were measured for 15 leaf and stem characters. Multivariate analysis (ordination) of the data from each cross placed the seedlings in relation to their parents, with most crosses intermediate, albeit closer to the maternal parent. Successful hybridization occurred within sect.Bisectaeser.Subulataeand between ser.Subulataeand sect.Bisectaeser.Kruseanae, ser.Levispermae, ser.Curviptera, ser.Erectaeand sect.Adnatariaser.Heterophloiae. In contrast, crosses between sect.Bisectaeser.Subulataeand sect.Adnatariaser.Aquilonaresand ser.Melliodoraedid not produce hybrids. Crosses between closely related species showed a greater degree of success than those between distant crosses, as did those between species with similar flower size.