Common name: Andean walnut

Andean walnut is a timber and nut-bearing tree native to the highlands of Colombia, Ecuador, Peru and Venezuela. Close relatives include the North American walnut (Juglans nigra) and English walnut (Juglans regia), both highly prized nut-bearing and timber trees originating in cold climate regions in North America, Europe and Western Asia.

Under favourable conditions, it is a fast-growing tree, to heights of up to 30 m (98 ft), though it is more typically 15 to 20 m (50 to 65 ft) tall. The trunk usually is straight, with a diameter of up to 90 cm (35 in), sometimes with a small buttress on large trees, and supports an irregular or rounded crown of ascending branches. The bark is thick, brown and slightly fissured.

The leaves are large, up to 40 cm (1.3 ft) long and made up of many oval, pointed and serrated leaflets arranged in pairs along the length. They remain on the tree throughout the year, though some leaf fall occurs in areas at the drier end of its rainfall range.

Around spring, it blooms small cream-coloured flowers on long slender clusters known as catkins, and with female and male flowers borne on separate catkins on the same tree. 

Fertilised female flowers develop into egg-shaped fruit, 2.5 to 4 cm long, green when young becoming yellow when mature with a thick, pulpy rind. The rind covers a wrinkled brown nut with a single oil-rich kernel inside. They ripen in summer, about three months after fruit-set, then fall to the ground where the rind gradually blackens. 

Use

The fruit are collected after they have fallen to the ground and soaked in water for one to two days for the rind to soften, making it easier to extract the nut. The nuts are then air-dried in the shade.

The nutshells are an important traditional dye source for the Altiplano weavers of northern Ecuador, who can extract a range of colours, from a deep chocolate brown to beige.

It produces a medium-weight wood, averaging out at around 600 kgs per cubic meter (38 lbs per cubic ft), classifying it as a hardwood. The heartwood is chestnut- to chocolate-brown, generally darker than North American walnut and sometimes has a purplish tinge. Its natural durability to rot, decay and wood-boring insects is not well researched.

Suitable logs are sawn into lumber to make furniture and cabinets, musical instruments, or thinly sliced for decorative veneers. Small diameter pieces are used for carvings, general woodcraft or firewood.

The leaves and rind covering the nut of Juglans species have long been used for dyeing fabric in shades of beige, brown and yellow and without needing a mordant for colour-fastness due to the usual high tannic acid content of the dye material. An iron modifier is sometimes added to the dye liquor to give richer, darker shades of brown.

The tree's over-exploitation for its wood has led to it being listed as endangered by the International Union for Conservation of Nature and Natural Resources  (IUCN), bringing attention to the need to protect the few remaining wild trees.

Health use

Walnuts are rich in edible oils, primarily polyunsaturated fatty acids with reasonable amounts of linolenic acid, an omega-3 fatty acid essential in human diets. Diets high in polyunsaturated fatty acids are known to help lower blood cholesterol.

Climate

Unlike its cold climate relatives, the Andean walnut does not require chilling to break dormancy. It grows naturally in humid subtropical and tropical mid- to high-elevation climates, generally areas with annual lows of 8 to 18°C, annual highs of 18 to 28°C, annual rainfall of 900 to 3000 mm and a dry season of 3 months or less.

Growing

New plants are usually started from seed. The trees performs best on deep, rich, freely draining clay, loam and sand soils of a moderately acid to neutral nature, generally with a pH of 5.0 to 7.0, and on sites with full to partial sun exposure. It has poor tolerance to poor, alkaline or limestone soils.

Problem features

It is recorded as an introduced tree species on the Galapagos islands and as a weed of the natural environment in Australia. Still, there does not appear to be a record of it anywhere as a serious weed.

Books

• Dean, J. 2010, Wild Color : the complete guide to making and using natural dyes (Revised and updated edition), Watson-Guptill Publishing, New York

• Green, C. L. 1995, Natural colourants and dyestuffs : a review of production, markets and development potential, Food and Agriculture Organization of the United Nations (FAO), Rome

• Jelks, Mary 1986, Allergy plants : that cause sneezing and wheezing, 1st ed., World-Wide Publications, Tampa, Florida

• 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

• Martin, F. M., et al. 1987, Perennial edible fruits of the tropics : an inventory, U.S. Dept. of Agriculture (USDA), Agricultural Research Service, U.S. Government Printing Office (GPO), Washington, D.C.

• National Research Council (Board on Science and Technology for International Development) 1989, Lost Crops of the Incas: Little-Known Plants of the Andes with Promise for Worldwide Cultivation, The National Academies Press, Washington D. C.

• Randall, R. P. 2002, A global compendium of weeds, R.G. and F.J. Richardson Press, Melbourne

• Randall, R. P. 2007, The introduced flora of Australia and its weed status, Cooperative Research Centre for Australian Weed Management, Glen Osmond, South Australia

• Record, S. J. & Hess, R. W., 1972, Timbers of the New World, Yale University Press, New Haven, Connecticut & Arno Press, New York

• Rosengarten, F. 1984, The book of edible nuts, Walker and Company Publishing, New York

• Vozzo, J. A 2002, Tropical tree seed manual, U.S. Department of Agriculture (USDA), Forest Service, Washington D.C.

• Wickens, G. E 1995, Edible nuts, Food and Agriculture Organization of the United Nations (FAO), Rome