Breeding system, reproductive efficiency and weed potential of Acacia baileyana

Acacia baileyana F. Muell. is a native environmental weed which has invaded bush areas of south-eastern Australia from ornamental plantings. There are two main colour forms, the typical green-leaf form and the variety 'purpurea', which has purple new growth. Only the green form appears to have invaded natural bush. The weed potential of A. baileyana was investigated in terms of its breeding system and seed production. It was found that the purple form is as reproductively efficient as the green form. Both forms were outcrossing, highly self-incompatible, grew very rapidly and flowered by two years of age. For open, natural pollination, final pod set was low-less than 0.41%. However, seed production was high due to the high number of flowers present. Maximum flower production for a 2-year-old plant was over 300 000, resulting in more than 8000 seeds. Precocity and high flower numbers appear to be the reasons for the weed status of A. baileyana. Given the similarity in reproductive efficiency between both forms, it is postulated that the absence of the purple form as a weed could be due to it being a relatively new horticultural variety, or to the purple colour being a recessive trait.