Interspecific hybridization within Eucalyptus (Myrtaceae): Subgenus Symphyomyrtus, sections Bisectae and Adnataria

The potential for interspecific hybridization within the genus Eucalyptus w as investigated through controlled pollination and measurement of seedling leaf morphology. Eucalyptus gillii and E. socialis (subgen. Symphyomyrtus s ect. Bisectae ser. Subulatae) were used as the female parents, and pollen w as sourced from 16 Eucalyptus species from a number of series within sectio ns Bisectae and Adnataria (subgen. Symphyomyrtus). Thirty-four out of 36 cr osses produced seeds; however, the percentage of seeds produced per flower pollinated varied considerably between crosses, as did germination percenta ge and seedling survival. At 3 mo of age, all surviving seedlings were meas ured 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. Suc cessful hybridization occurred within sect. Bisectae ser. Subulatae and bet ween ser. Subulatae and sect. Bisectae ser. Kruseanae, ser. Levispermae, se r. Curviptera, ser. Erectae and sect. Adnataria ser. Heterophloiae. In cont rast, crosses between sect. Bisectae ser. Subulatae and sect. Adnataria ser . Aquilonares and ser. Melliodorae did not produce hybrids. Crosses between closely related species showed a greater degree of success than those betw een distant crosses, as did those between species with similar flower size.