Friday, November 30, 2012

Black Bean

Castanospermum australe

It takes a few years to see a reward, when we plant rainforest trees, but black beans are among the ones which put on a good show while still quite young. This lovely specimen in Highfields has been flowering for several years now. I don’t know it’s age, but it’s probably about 10 years old. The species is great value for a larger garden. It will grow quite fast to make a medium to large tree - about the size of the familiar camphor laurels, which are used as street trees in Toowoomba. It's dense, dark green canopy makes it a very good shade tree.

 The flowers appear on old wood, inside the canopy.

Flowers at all stages of development are on the tree at the same time, and make a perfect illustration, if you happen to be wanting to teach children how flowers “turn into” seeds.

These little green pods will develop into large brown seedpods, whose huge seeds will germinate if left sitting on damp soil in a pot - another interesting thing for children to see. They can use the pods as boats, once the seeds have been taken out. The circular depressions left by the seeds make good “seats” for tiny toys.
The special shape of the flowers shows us that the plant wants to attract nectar-eating birds as pollinators. The jacaranda in the background (an introduced tree, native to Amazon rainforests) has very little appeal to wildlife. The black bean, however, is pulling its weight as an active contributor to a healthy suburban environment.
It is drought hardy in the Toowoomba area, and tolerates light frosts.
For more on this plant, see Nov 2009 (or use the “search” box, at top left).

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