Castanospermum australe

Castanospermum australe.

The Black Bean is in Family Fabaceae s.s. (Family Fabaceae s.l. > Subfamily Faboideae).
The only species in the genus, it is native to eastern Queensland and N.S.W.

They are evergreen trees growing 15 to 20 m high in cultivation but can be up to 40 m.
The canopy is rounded and dense with shiny, dark green foliage.
The small branches are covered in lenticels.

The alternate, pinnate leaves are around 40 cm long.
Each has 11 to 15 alternate leaflets up to 15 or 20 cm long, on short petiolules.

Inflorescences are small spikes of flowers on bare wood along the branches.
Each spike is up to 6 cm long.
The bisexual flowers are 3 or 4 cm long with parts in 5’s.

The cup-shaped hypanthium is formed by fusion of the bases of the sepals, petals and stamen filaments.
The nectaries line the inside of the hypanthium.
Flowers are on stalks 2 to 2.5 cm long with deciduous bracteoles at the base.

On the hypanthium rim are the small, triangular sepal lobes.
The hypanthium, and sepal lobes are 1 to 1.5 cm long.
The sepals have some short hairs externally but more internally.
The lobes persist on the immature fruit then fall off.

The bi-lobed upper or banner petal is the largest.
It is 3 to 4 cm long and curves backwards.
The other 4 petals are free and all similar.
They are around 2.5 cm long and narrowly ovate or obovate with a pointed tip.
When the flower is mature the initially yellow petals change to orange then red.
The petals are thick and slightly fleshy.

There are 10 free stamens that extend beyond the corolla.
The dorsifixed anthers open via long slits.
The ovary is on a long stalk or gynophore that inserts into the base of the hypanthium.
There is a style, yellow then red, with a small stigma.

The hard brown fruit pods are up to 20 cm long and 6 cm thick.
They split down both sutures to reveal 1 to 5 large seeds each in a cell.
The roughly spherical seeds are a shiny brown and up to 3 cm across.
Mature fruit fall off rather than remain on the tree and they cover the ground underneath.