Castanospermum spp.

black bean

Fabaceae

Eastern Australia and the southwestern Pacific

Attracts Pollinators Container Friendly

SunFull Sun – Part Shade

WaterMedium

HardinessZones 10–11

Overview

Castanospermum spp. is a genus in the pea family (Fabaceae) with a single species, the black bean or Moreton Bay chestnut, Castanospermum australe, a large evergreen tree of eastern Australian rainforests. In the wild it grows 30-130 feet (9-40 m) tall with a dense, rounded crown of glossy, pinnate leaves, each made up of nine to seventeen leaflets. In late spring and summer clusters of bright red-orange and yellow pea flowers open directly on the older branches and trunk, a habit called cauliflory, and these draw nectar-feeding birds. The flowers form very large woody pods 4-9 inches (10-23 cm) long, each holding three to five chestnut-sized seeds. The seeds are toxic raw, containing saponins and the alkaloid castanospermine, and were eaten by Aboriginal Australians only after long leaching and roasting. Young plants are widely sold as indoor foliage plants grown from the big seeds. The tree needs a frost-free climate and ample room and root space, which limits its use as a landscape tree to mild regions.

Native Range

The black bean is native to the coastal rainforests and riverbanks of eastern Australia, from New South Wales to far north Queensland, and to parts of the southwestern Pacific including Vanuatu and New Caledonia. It grows in warm, moist lowland forest, often along streams.

Suggested Uses

In frost-free climates the black bean is grown as a large shade and street tree where there is room for its size and roots. The glossy pinnate foliage also makes it a long-lived indoor and conservatory plant while young. The timber is worked for furniture and cabinetry, and the seeds are studied as a source of castanospermine.

How to Identify

Look for a large evergreen tree with glossy, dark green pinnate leaves divided into several broad leaflets. The clearest sign in season is the bright red-orange and yellow pea flowers borne in short clusters straight from the trunk and older branches. These give way to heavy, woody pods up to 9 inches (23 cm) long that hold a few large, rounded brown seeds.

Appearance

Size & Dimensions

Height30' - 130'

Width/Spread20' - 50'

Reaches mature size in approximately 20 years

Colors

Flower Colors

red

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~4 weeks

Spring Summer

Flowering comes in late spring and summer, around November to January in the native range, with red-orange and yellow flowers clustered on the trunk and main limbs. Nectar-feeding birds, including parrots and honeyeaters, visit the flowers and carry the pollen. Large woody pods then develop over the following months and split open when ripe to drop the big seeds.

Detailed Descriptions

Flower Description

red-orange to yellow

Foliage Description

glossy dark green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 6-10 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 7.0(Neutral)

357912

Soil Types

loam clay

Drainagemoist

Water & Climate

Water Needs

Medium

Frost Tolerance

tender

Time to Maturity

slow; flowers after about 8-12 years

Care & Maintenance

Care Guide

The black bean grows in full sun to part shade on deep, moist, fertile, well-drained soil with a pH of about 5.5 to 7.0. Warmth is needed, as the tree is frost-tender and suited to subtropical and tropical climates. Regular water suits it, matching the moist forest and streamside habitats where it grows wild, though established trees handle short dry spells. Growth is slow, and trees take many years to flower, so the species is grown as much for foliage as for bloom. As young plants it grows well indoors in bright light, raised from the large seeds in containers of free-draining mix. The big roots and eventual size mean garden trees are set well away from paving and pipes.

Pruning

Little pruning is needed beyond removing dead or crossing branches and shaping young trees. Any cutting is done after flowering or in the warm season when the tree heals fast. Indoor plants are tip-pruned to hold them compact and bushy.