Castanospermum australe aka Moreton Bay Chestnut

Castanospermum australe belongs to the pea family. This tree stays green all year. People call it black bean or Moreton Bay chestnut. Kew lists eastern Australia and Vanuatu as its native range. In Australia, it grows from Queensland into northeastern New South Wales. Other sources list New Caledonia as part of its range. It grows in tropical and subtropical rainforest, often near creeks. These sites provide rich soil and a steady supply of water.

The tree grows slowly and forms a dense crown. Its leaves are dark green. Sources give heights of about 66–82 feet [20–25 metres]. Wider accounts report heights of 115–131 feet [35–40 metres]. Reported widths range from 16–39 feet [5–12 metres]. One profile gives a spread of 66 feet [20 metres]. The trunk grows upright, with smooth grey to brown bark. The leaves shine and stay on the tree year-round. When crushed, they give off a scent like cucumber.

The flowers look like pea flowers and grow in groups. They draw birds that pollinate them. Their colours range from yellow and orange to orange-red. PFAF gives September to October as the bloom time. Large pods hang from the tree after the flowers. They hold several seeds. Each pod is about 4–10 inches long, with three to five seeds. Each seed is about 1–1.8 inches across. The flowers and fruit make it useful as an ornamental tree. In warm regions, people plant it as a specimen or street tree.

The tree needs moist, rich soil that drains well. It grows in sand, loam or clay. Acid soil suits it best. PFAF also lists neutral soil as suitable. It needs sun, with a sunny site stressed in cooler climates. PFAF lists USDA zones 8–12 but calls it a warm-climate tree. Its wide roots help protect riverbanks and catchment land. The tree fixes nitrogen and draws wildlife. Its hard, heavy wood resists rot. People use the wood to build and as fuel.

People have used the seeds as food in the past. The seeds need a great deal of treatment before eating. Cooking alone is not enough. Sources disagree on whether raw, ripe seeds are safe. Both warn that seeds are poisonous and need processing. Seeds with no treatment can cause severe gut upset. Past users soaked them for a long time, then roasted and ground them. Researchers have studied castanospermine, a seed compound, for possible medical uses. That work does not show that it is a safe home remedy.