Common name: Queensland walnut

Queensland walnut is a timber tree originating in the Daintree rainforest in Queensland, Australia, prized for its decorative wood used to make fine furniture and cabinets. 

It is a large tree, up to 40 m (130 ft) tall in closely spaced forest, typically with a straight, well-formed trunk up to 2.2 m (7.2 ft) in diameter. Usually buttressed at the base and branch-free for more than half of the tree height, the trunk supports a densely branched, narrowly rounded crown. The bark is relatively smooth, pale grey to brown, becoming flaking, mottled and rough on older trees.

The adult leaves are oval to elliptical, 8 to 17 cm (3 to 6.7 in) long, dark glossy green, and spirally arranged along the stems at the ends of the branches. They remain on the tree throughout the year.

The flowers are bisexual, creamy-white, small and held in branched clusters arising at nodes along the branches. They bloom from spring through summer and are followed by round, ribbed fruit up to 7 cm (2.8 in) in diameter. Green when young, they become yellow to pale orange when mature and contain a single, round, nut-like seed up to 4 cm (1.6 in) in diameter.

Use

Queensland walnut produces a medium-weight wood, in the 550 to 770 kg per cubic meter (34 to 48 lbs per cubic ft) range, with low natural resistance to rot, decay and termites. This puts it in the non-durable hardwood class, suitable only for indoor use. The heartwood is chocolate brown to black-brown with decorative streaking and is comparable to English walnut (Juglans regia) in appearance.

Well-formed logs are sawn into planks for making fine furniture, cabinets and for interior joinery and flooring. Selected logs are sliced into thin decorative veneers, mostly face veneers for plywood, parquetry and marquetry. The wood's excellent tonal qualities also make it suitable for making guitars. Small diameter roundwood lengths are highly sought after for woodturning, carving and woodcraft generally. However, the wood is highly abrasive due to its high silica content, quickly dulling cutting saws and blades.

The seed are reportedly edible and eaten as a nut after roasting, with a taste described as similar to the common walnut.

Climate

Grows naturally in moderately humid to very humid subtropical and tropical mid- to high-elevation climates, generally areas with annual lows of 13 to 20°C, annual highs of 24 to 30°C, annual rainfall of 1300 to 3800 mm and a dry season of 4 months or less. However, it reaches its best development as a timber tree in areas with annual rainfall of 1600 mm or more.

Growing

New plants are usually started from seed, collected from the ground after the fruit falls from the tree. Performs best on deep, rich, free-draining clay and loam soils of a moderately acid to neutral nature, generally with a pH of 5.0 to 7.5, and on sites with full to partial sun exposure.

Problem features

There does not appear to be any record of it anywhere as a problem weed or invasive species. The fruit are single-seeded and fall close to the parent tree, and the large seed makes widespread dispersal unlikely. Further, any animals eating the seed would probably destroy it, making it unlikely to become a weed. 

Books

• Boland, D. & Brooker, I. & McDonald, M. W. 2006, Forest trees of Australia, 5th ed., CSIRO Publishing (Ensis), Melbourne

• Bristow, M. & Bragg, A. & Annandale. M. 2005, Growing rainforest timber trees: a farm forestry manual for north Queensland, Research and Development Corporation (RIRDC), Barton, A.C.T, Australia

• Chudnoff, M. 1984, Tropical timbers of the world, Forest Service, U.S. Department of Agriculture (USDA), Washington, D.C.

• Kukachka, B. F & Forest Products Laboratory (U.S.) 1970, Properties of imported tropical woods, United States, Department of Agriculture, Forest Service, forest Products Laboratory, Madison

• Lake, M. 2015, Australian rainforest woods : characteristics, uses and identification, CSIRO Publishing, Collingwood, Victoria

• Menninger, E. A. 1977, Edible nuts of the world, Horticultural Books, Stuart, Florida

• Porter, T. 2012, Wood : identification & use, Compact edition, Guild of Master Craftsman Publications, Lewes, East Sussex

• Scheffer, T. C & Morrell, J. J. 1998, Natural durability of wood : a worldwide checklist of species, Forest Research Laboratory, Oregon State University, Corvallis, Oregon