The Seedpods of the Invasive Australian Blackwood

The Australian Blackwood (in the Mimosa family) is cultivated in a range from California to Chili, but in most of these areas, the tree has spread further than it was originally intended, making it an invasive species. The dispersal of the seeds of the tree is largely responsible for its ability to spread into new areas. The seedpods are contained in long, thin ribbon-like beans that are coral colored. Once the beans dry, they split and the seeds are projected in many directions.

In both Australia and South Africa, birds are attracted to the reddish-orange seed stalk, called an aril, which they consume – thus dispersing the seed widely throughout the birds’ habitat. South Africa has declared the Australian Blackwood a noxious weed species and has been seeking ways to control it. Presently, it has introduced a seed-feeding weevil to counteract its spread.

Ants are also attracted to the aril because it is rich in protein. The ants eat the arils and discard the seeds – usually in the nest or on a rubbish heap – where they are in a good environment for future germination. They can have a long dormancy. The seed has a hard coating for bushfire germination and may be viable for up to 50 years, while the tree itself has a lifespan of over 100 years, so it can produce many seeds during its lifetime.