Reproductive biology and interspecific hybridisation of Acacia mangium and Acacia auriculiformis A. Cunn. ex Benth. (Leguminosae: Mimosoideae).

Abstract

A study was made of the reproductive biology of Acacia mangium and A. auriculiformis growing at Atherton in Queensland, and near Kuala Lumpur in Peninsular Malaysia, and Tawau in Sabah. Both species flowered between February and May, producing mature pods between October and April. The flowers of both species were similar in structure and showed weak protogyny and variable levels of andromonoecy. Male flowers either lacked pistils completely or had small sterile pistils. Controlled hand pollination resulted in pollen tubes in the pistil and penetration of the ovules following self and cross intraspecific and interspecific pollination. The cross A. auriculiformis × A. mangium was more successful than the reciprocal, but fertile seed was produced following interspecific pollination in both directions and all seedlings were shown to be hybrid by isoenzyme analysis of parent and seedlings. There were relatively few insect visitors to the flowering branches, but the same suite of insects was observed foraging for pollen on both species. Native bees belonging to the Halictidae carried most polyads on their hairy bodies and may act as pollinating agents. There appeared to be no major fertility barriers to interspecific hybridization between A. mangium and A. auriculiformis, and hybrids could occur spontaneously via synchronous flowering and common insect visitors.