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Plant of the month August

Common Name: Black Bean, Moreton Bay Chestnut

Scientific Name: Castanospermum australe A.Cunn. ex Mundie

Family: Fabaceae - Faboideae

 

Etymology

Genus:  

From castanea latin for chestun and spermum Greek for seeded

Species:

australe - latin for southern

Distribution

East coast of Australia from Lismore, NSW to the Iron Range Cape York, Qld and 160 km west to the Bunya Mountains. Also found in New Caledonia and Vanuatu.

Native Habitat

Coastal rainforest in moist fertile soils often along the banks of rivers or streams.

Description 

A large evergreen tree to a height of 40 m with trunk to 1.5 m and a broad umbrageous crown. Glossy, dark green pinnate leaves 30-60 com long with 9-17 leaflets.

Flowers 

Sprays of red and yellow pea-shaped flowers, 3-4 cm long occur in late spring and early summer. They are rich in nectar and attract many pollinators including Rainbow Lorikeets and Grey Headed Flying Foxes.

Fruit

Large cylindrical pods, 12-20 cm long are produced from autumn to winter. These pods split in two, revealing 3-5 cm large bean like seeds weighing about 30 grams. Seeds are poisonous, not eaten by native animals and float. The chemical compound, Castanospermine was extracted from the seeds and research is ongoing into its use in inhibiting viruses such as HIV and Dengue Fever.

Location in Garden

Australian rainforest (bd 65i), Lower garden lawn 25.

Information

Recently our Evolutionary Ecology team working with Aboriginal cultural groups in northern NSW, have shown that the unusual distribution pattern of this tree in NSW, is the result of Aboriginal people deliberately dispersing seeds to new places. Although the seeds are toxic, Aboriginal people, for over 2500 years, have understood how to leach the toxins from the seeds and by subsequent roasting create an edible damper (bread).

Dr. Maurizio Rossetto and his team study the factors that influence the distribution of Australian plants, by looking at genetic variation within and between populations. When they examined the DNA from Black Bean trees in northern NSW, they found very low genetic diversity among the many populations that grow from the coast to 100 km inland, and upland 100 m from natural water courses. Essentially all these trees are derived from a single parent, from seeds moved by Aboriginal people in the last few thousand years.

This scientific story of the tree’s journey through NSW converges with traditional Songlines and stories shared by Aboriginal cultural groups in northern NSW, part of the oldest continuous human culture on earth.

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