Iconic creek bank tree

Large tree to 40 metres, often occurs in stands. Black Bean grows well along the banks of rivers and creeks. It has a strong root system, which can be used to consolidate stream banks against erosion. In the garden it rarely grows more than 20 metres with a dense crown.

Medicinal and other uses

Reported as a food source after treatment to remove the poison. According to Tim Low in Bush Medicine Aboriginal people “found ways of leaching away the toxins by grating, soaking and baking”. Reports in 2025 said research into Castanospermum australe had identified a unique alkaloid called castanospermine which has active pharmaceutical potential against viral infections, metabolic disorders and diseases spread by living animals such as mosquitoes.

Flowering, mature Castanospermum australe at Walton Bridge Reserve, October 2025. Noisy Friar Birds, Blue-faced Honeyeaters and Rainbow Lorikeets were feasting on the flowers. Photo: Anne Jones

Leaves. Photo: Robert Whyte

Flowers

In November it has sprays of red and yellow pea-shaped flowers 3-4 cm long. The nectar produced by the flowers attracts birds especially King Parrots, bats and butterflies. Spangled drongoes nest in them when they send their summers on Enoggera Creek. Host plant for larvae of Common Pencilled-blue Candalides absimilis. The timber was much sought after in times gone by, but is rarely harvested now.

Flowers. PHOTO: Matt Tomkins

Seeds and seed cases

The seeds are typical (if large) beans. They fall in large seed cases and get transported by floods to other locations along the creek, or else germinate in great numbers around the parent trees. It is better to sow the seed directly into the desired location, as it does not like transplanting. It starts off better in shade, then searches for the sun.  The seed cases make good toy boats.

Seeds and pods. The seeds are about the size of a golf ball 30-50 mm long and 30-40 mm wide. Pods hold 1-6 seeds. Photo: Robert Whyte

The unripe seed contains saponin (a poison) which can be used to stun fish, but Jagera pseudorhus was more often used in this way. Seeds are easy to collect and certainly make an impact on the seed inventory when measured by weight. Common names include Moreton Bay Chestnut, Moreton Bay Bean, Bean Tree, Mei, Wild chestnut, Wombai. Castanospernum from Greek kastanon, the chestnut tree and sperma seed of plants, referring to the similarity in appearance of the seed to that of a chestnut. Australe Latin, southern.

Photo: Robert Whyte

Seed collecting and propagation

Seeds are ripe in February to April when the pods crack open naturally. Seeds require no treatment. Sow them direct into 10 cm pots or into the ground in sight of the creek bank. When sowing in pots, leave half the seed exposed, with the groove vertical and the nipple (where it was connected to the seed pod) facing down.