Tung Oil Tree Photos

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Economic Plant Photographs: Tung Oil Tree

Tung Oil Tree, Candlenuts & Kukui Nuts

Tung Oil Tree

Tung oil comes from the seeds of several species of Aleurites, primarily Aleurites fordii, a deciduous shade tree native to China. It belongs to the Euphorbia Family (Euphorbiaceae) along with the candlenut tree (A. molucanna), another species with seeds rich in unsaturated oils. For centuries tung oil has been used for paints and waterproof coatings, and as a component of caulk and mortar. It is an ingredient in "India ink" and is commonly used for a lustrous finish on wood. In fact, the "teak oil" sold for fine furniture is usually refined tung oil. Some woodworkers consider tung oil to be one of the best natural finishes for wood.

Tung oil tree (Aleurites fordii) showing two male flowers and one female flower (left) in which the petals have fallen off exposing the pistil.

Other unsaturated plant oils, such as castor oil and linseed oil, take longer to dry and leave an oily residue until they soak into the wood surface. Tung oil 's ability to dry quickly and polymerize into a tough, glossy, waterproof coating has made it especially valuable in paints, varnishes, linoleum, oilcloth and printing inks.

Fruit and seeds of the tung oil tree (Aleurites fordii). The oil-rich seeds are the source of tung oil used on fine furniture. The lower left fruit has completely dried out.

Tung oil tree (Aleurites fordii). According to Systematic Treatment of Fruit Types by Richard Spjut (Memoirs of New York Botanic Garden, Volume 70, 1994), the fruit is a "bacca." It is technically not a drupe because it lacks a stony endocarp.

The pit of a peach (Prunus persica) showing the seed that is contained inside the hard, woody endocarp layer. The endocarp is the inner layer of the fruit wall or pericarp. It is surrounded by a fleshy mesocarp and a thin outer skin or exocarp. Fruits with an endocarp layer surrounding the seed are called drupes or drupaceous. The endocarp protects and aids in the dispersal of the vulnerable seed, especially when it is swallowed by a hungry herbivore.

See Drupaceous Fruits & Nuts Defined

Tung oil is composed primarily of eleostearic (elaeostearic) acid, with smaller amounts of oleic, linoleic and palmitic glycerides. Eleostearic acid is a crystalline unsaturated fatty acid that exists in 2 stereoisomeric forms: An alpha acid occurring as the glycerol ester especially in tung oil, and a beta acid obtained from the alpha acid by irradiation (9, 11, 13-octadecatrienoic acid). The following table shows the chemical structure of tung oil eleostearic acid:


See Chemistry Of Unsaturated Plant Oils
See Article About The Castor Bean Plant

Candlenuts And Kukui Nuts

Although the closely related candlenut tree (Aleurites molucanna) is also native to Asia, it has been spread by people throughout the tropical Pacific because its seeds are rich in oil. The valuable oil expressed from seeds is used as a light source and as a mild cathartic. Seeds were strung together and burned like a candle.

The seed of candlenut (Aleurites molucanna) contains about 50 percent oil. This is why it ignites and burns like a candle. The ancient Polynesians brought this tree to the Hawaiian Islands where it has become naturalized. The dried nuts were cracked open and the seeds were skewered onto the midrib of a coconut frond (or slender bamboo stem) and set on fire. The Polynesians used them for candles that burned for about 45 minutes. Hawaiians also extracted the oil for many other uses: to shine and waterproof wooden bowls, to mix with charcoal to make black canoe paint, to burn as torches, and to burn in stone lamps for light.

Shelled candlenuts (Aleurites molucanna) are commonly sold in Asian food markets. Although they superficially resemble shelled macadamia nuts, they should not be eaten raw because they contain a strong purgative. Apparently roasted seeds are eaten, but only in small quantities because of their laxative effect. In Hawaii they are roasted and made into a condiment called inamona, by pounding them into a paste that is mixed with salt. The inamona paste is mixed with seaweed, minced chile peppers and bite-sized cubes of raw ahi fish (or another fish) to prepare a favorite Hawaiian dish called "inamona poke." The cooked, mashed seeds are used in a similar Indonesian dish called "sambal kemiri." Candlenut paste is also used to thicken and flavor Indonesian and Malaysian curries.

A bag of shelled candlenuts (Aleurites molucanna). The shelled nuts are actually the seeds of this tropical Malaysian tree. Like the label states: This is not a snack food. The ground nuts are used in the preparation of several Asian and Polynesian dishes including a thickener and flavoring in Indonesian curries.

In the Hawaiian Islands candlenuts are known as "kukui nuts" and are polished and made into shiny dark brown or black bracelets and leis. The fruit of kukui nut or candlenut (Aleurites molucanna) is usually classified as a drupe or drupaceous nut, but the actual "nut" is really a woody, thick-walled seed, typically one or two inside each fruit. According to Spjut (1994), the kukui nut fruit is a "bacca" or berry-like fruit: An indehiscent simple fruit containing one or more seeds embedded in a solid, fleshy mass supported by epicarp less than 2 mm thick, the pericarp not differentiated internally by a hardened endocarp or air space.

A nut may be defined as a one-seeded fruit with a hard pericarp (ripened ovary wall).  One or several nuts may sit in a cup-shaped structure called an involucre. In oaks (Quercus) the involucre is composed of small scales and the entire structure (involucre plus nut) is called an acorn. In chestnuts (Castanea) and beech (Fagus) the involucre is spiny, while in filberts and hazelnuts (Corylus), the involucre is leafy or tubular, depending on the exact species.

This is a simplified classification of dry fruit types that follows most general botany textbooks and plant identification manuals. There are many fruits that don't exactly fit the nut or drupe categories. For an in-depth study of these fruit types, please refer to the A Systematic Treatment of Fruit Types by Richard Spjut (Memoirs of New York Botanic Garden, Volume 70, 1994). This scholarly article is based on extensive research of classical fruit nomenclature dating back to the 18th century. Unfortunately it does not use the term "nut" as a distinct fruit type.

Hard-shelled kukui nuts take such a brilliant luster that they resemble polished gemstones. There are several variations in the polished nuts, including smooth and grooved. Color variations include black, brown, light brown, marble and white. The nuts are strung whole, half-shell, or in fragments of the seed shell. A step-by-step guide on how the kukui nuts are drilled and strung onto satin ribbon is explained in Hawaiian Seed Lei Making by Laurie S. Ide (2001). Throughout the islands the light green (silvery-gray) foliage decorates lush canyons and valleys. The light-colored foliage is easy to spot from the numerous vistas on these lovely islands. Candlenut seeds occasionally drift ashore on islands of the Caribbean and are known locally as "Jamaican walnuts" because of their superficial resemblance to an unshelled walnut.

A black kukui nut necklace, made from the polished, thick-shelled "nuts" (seeds) of the candlenut tree (Aleurites molucanna). In Caribbean waters the durable drift seeds are known as "Jamaican walnuts."

A brown kukui nut necklace, made from the polished, thick-shelled "nuts" (seeds) of the candlenut tree (Aleurites molucanna). In Caribbean waters the durable drift seeds are known as "Jamaican walnuts."

A Hawaiian kukui nut necklace, made from the polished, thick-shelled "nuts" (seeds) of the candlenut tree (Aleurites molucanna). The green fruit is cut open to show the brown, thick-walled seed. The fruit superficially resembles a green walnut; however, the walnut is technically a "pseudodrupe." Several rough, woody "nuts" (seeds) are shown before polishing.

The candlenut tree (Aleurites molucanna).

Colorful Hawaiian necklaces, made from painted and polished kukui "nuts."

According to the United States National Herbarium, the official state tree of Hawaii is the kukui nut. Unlike the state flower, the yellow Hibiscus brackenridgei, Hawaii's official state tree is not native to the Hawaiian Islands. The kukui nut was legislated in 1959 because of its historial significance in the colonization of Hawaii by native Polynesians. Today it is a widespread tree throughout the islands.

Clumps of silvery-green kukui nut trees on the steeps slopes above rain-soaked Iao Valley on the Hawaiian Island of Maui.

Leaves of the kukui nut tree glow transparent green against the sky.

Left: Unpolished kukui nuts (Aleurites molucanna) washed ashore on a Maui beach. Right: A polished kukui nut bracelet. Althought it is not native, the kukui nut tree has been designated the official state tree of Hawaii.

See Botanical Jewelry Article

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