The black bean is a small, black variety of the common bean popularly used in Latin American cuisine. Black beans, like most other legumes, are rich in cholesterol-lowering fibre, which also prevents blood sugar levels from rising rapidly after dining, making these beans a good choice for diabetes sufferers.
Black beans are also a great source of high quality, virtually fat-free protein.
From what I read, Castanospermum australe is called a blackbean, but it is a tree, and its seed is NOT the edible black bean you refer to here. The blackbean tree doesn't even grow in latin america, and its seeds are poisonous unless carefully treated.
Of course, my source could be wrong, but perhaps you should check.