Castanospermum australe

black bean tree


Castanospermum australe

A.Cunn. & C.Fraser 1830

pronounced: kass-tah-oh-SPER-mum oss-TRAH-lee

(Fabaceae — the pea family)


common names: black bean, Moreton Bay chestmut

native 4Castanospermum is derived from the Latin castanea, the chestnut, and the Greek σπερμα (sperma), a seed; australe is from the Latin australis, south. This magnificent tree occurs on Cape York Peninsula and in discrete colonies down the Queensland coast and, more rarely, on the NSW coast near Lismore.

This plant is one of those collected in 1770 by Banks and Solander during the voyage of the Endeavour. It was collected at the Endeavour River (Cooktown).

It is the only species in its genus, and is native to coastal rainforests, growing in moist, fertile, well-drained soils on mountainside terraces or along the banks of streams. It is also found in New Caledonia and Vanuatu.

At maturity it can reach a height of 40 m, with a beautiful straight trunk.
The specimen photographed, in Andy Gabb’s garden in Arcadia, is lopped every couple of years to prevent it from overwhelming the garden.

This is a hardy species that is suitable for planting in a wide range of conditions through Australia, including in Melbourne, where it will grow to a height of about 8 m. It prefers full sun, although it will tolerate some shade, as well as light frost. Under cultivation it will develop a dense rounded canopy and reach a height of up to about 20 m, with a spread of 4 – 8 m. It is an ideal shade tree in parks and large gardens.

When grown in the open, this is a handsome tree with glossy dark green pinnate leaves and low spreading branches. The leaves are 30 – 60 cm long, with 9 – 17 leaflets, oblong-elliptic in shape, with acuminate apex, entire margins, glabrous, the upper surface glossy, the lower surface paler and dull; the petiole is 3 – 6 cm long, and the lateral petiolules 2 – 4 mm long.

During October and November it bears racemes 5 – 15 cm long, of red and yellow pea-shaped flowers 3 – 4 cm long, which are followed in March – May by large cylindrical pods 12 – 20 cm by 4 – 6 cm. Each flower has 10 stamens, and the ovary is on a long stalk.

The pods split in two, revealing 2 – 5 large chestnut-like seeds. The nectar produced by the flowers attracts large numbers of Rainbow Lorikeets (who often become drunk on the fermenting nectar), as well as bats and butterflies.

The fresh raw seed contains high levels of saponin, and can be harmful to animals and humans. The cooked seed tastes rather like a sweet chestnut, but requires considerable leaching before it is safe to eat. The indigenous peoples finely sliced the seeds and soaked them in running water for about 10 days before roasting them and grinding them into a powder, which they stored for later use.

The sapwood of this tree is white to yellow, distinct from the heartwood, which is dark brown to chocolate, sometimes with fine white streaks, and a prominent figure. Growth rings are absent. It is a very durable timber, with an above-ground life expectancy of over 40 years, and an in-ground expectancy of over 25 years. Untreated sapwood is susceptible to lyctine borer attack, and the timber is not resistant to termites. The sapwood readily accepts preservative impregnation, but penetration of the heartwood is negligible with currently available methods. Care is needed in seasoning the timber, as it shrinks irregularly and is prone to collapse. It is regarded as a moderately hard wood, and both machines and turns well to a smooth finish. The dust produced during working is a nose and throat irritant to some people. Due to its dark colour, staining is normally not necessary, but some preliminary filling may be necessary because of the coarse texture of the wood.

It was formerly much used as both sawn and round timber in bridge construction, and had limited use in house construction. It was popular for split timber fence posts on the Atherton Tableland during the days of early settlement, as there were few rainforest trees that could be easily split for that purpose. Now its use is mainly limited to turning, inlay work, carving and joinery.


Photographs taken in Arcadia 2013
Page last updated 2nd November 2018