Triadica sebiferum (PROSEA)
Triadica sebiferum (L.) Small
- Protologue: Man. of the Southeast. Fl. : 789 (1933).
- Family: Euphorbiaceae
- Chromosome number: 2n= 36
Croton sebiferum L.(1753), Stillingia sebifera (L.) Michx. (1803), Sapium sebiferum (L.) Roxb. (1832).
- Chinese tallow tree, candleberry tree (En). Popcorn tree (Am). Boiré, arbre à suif (Fr)
- Indonesia: kasumbi, kirendang (Java)
- Vietnam: cây sòi.
Origin and geographic distribution
T. sebiferum is native to China and probably also to Taiwan, where it is cultivated. In former times, it was grown more widely in South-East Asia. It used to be cultivated and was found naturalized in Indonesia (near Jakarta, Timor), Singapore, Indo-China and Japan. It has also been acclimatized in northern India and in north-western Pakistan where it was originally brought in as an ornamental tree. It was introduced into the United States in the late 18th Century as a wayside tree, was planted along the coast of the Gulf of Mexico in the early 20th Century and can now be found in the south-eastern states. T. sebiferum was also introduced into the former Soviet Union and is grown e.g. in the coastal areas along the Black Sea in Georgia.
The fruit of T. sebiferum contains two types of fat: the white, fleshy outer seedcoat (sarcotesta) produces a fat known as Chinese vegetable tallow or "pi-yu" in trade, while the cotyledons of the seed (kernel) yield a drying oil called stillingia oil or "ting-yu" in trade. Chinese vegetable tallow is widely used in China for edible purposes, as a substitute for animal tallow and tung oil, and for lighting. Candles made by mixing 10 parts vegetable tallow with 3 parts white insect wax are reputed to remain pure white for any length of time, to burn with a clear bright flame without smell or smoke and are used especially in Buddhist ceremonies. Elsewhere the vegetable tallow is used to make soap, as a substitute for cocoa butter and to increase the consistence of soft edible fats. Stillingia oil is used in paints and varnishes, for illumination and to waterproof umbrellas. Both the tallow and stillingia oil are used as fuel extenders on a small scale. The presscake remaining after tallow and oil extraction is unsuitable as feed for livestock because it contains saponins, but can be used as fuel or as manure. However, the presscake can be processed to make a valuable animal feed and human food, rich in protein. The leaves contain a dye, used in Indo-China and China to dye silk black. T. sebiferum is also an agroforestry species and an ornamental. It is a good soil binder and contributes to nutrient recycling. In tea plantations, it is planted as a shade tree against heat and desiccation. It is a minor timber tree: its wood has been used to make various implements, toys, furniture and Chinese printing blocks. Because T. sebiferum has a high woody-biomass production, it is potentially an important source of energy. In traditional medicine in China, the root bark is utilized for its diuretic properties and is said to be effective in the treatment of schistosomiasis. The leaves are applied to cure shingles.
Production and international trade
After the 2nd World War, when there was a shortage of linseed oil (which is the major drying oil for paints), interest in stillingia oil from T. sebiferum increased and the oil reached prices of UK£ 200 per t in the world market. Experimental plantations were established in several South-East Asian countries, but outside China the trials did not meet expectations. A serious obstacle in exploiting the tree commercially has been the large amount of labour involved in collecting the ripe fruits by hand, which often competes with more urgent activities on a farm. Hence, oil supply was irregular and limited; only China exported annually about 4000-5000 t. At present, almost all stillingia oil and vegetable tallow oil are produced and used locally in China. The annual tallow production has been estimated to be about 50 000 t; annual exports have been as high as 15 000 t but export is almost zero at present. Because T . sebiferum tolerates many unfavourable soil conditions and some frost, interest in it has grown again since the 1980s as a potential fuel and biomass producer in marginal soils particularly in the south-eastern United States. As an oil crop, it has always been considered unprofitable in the United States because of the difficulty of harvesting the seeds economically. Annual return per ha of tallow, oil and presscake together was estimated at US$ 750 in the 1980s.
The proportions of the different parts of air-dried seed (moisture content about 5%) of T . sebiferum are approximately: sarcotesta 30%, shell 40% and kernel 30%. The sarcotesta yields 50-80% vegetable tallow (whitish, hard, edible but tasteless) while the kernel yields 50-60% stillingia oil (strong smelling, not edible, emetic). The major fatty acid constituents of Chinese vegetable tallow are palmitic acid (60%) and oleic acid (30%). The principal glycerides are oleodipalmitin (60%), stearodipalmitin (10%), tripalmitin (10%) and oleopalmitostearin (10%). Its melting point is about 50°C.
The fatty acid constituents of stillingia oil are mainly unsaturated ones: oleic acid (20%), linoleic acid (25%) and linolenic acid (40%). The presence of unstable and easily oxidized estolides may explain why stillingia oil is a better drying oil than tung oil. Stillingia oil is poisonous and makes the vegetable tallow inedible if accidentally mixed with it. This oil also has inflammation and tumour-promoting properties.
The leaves of T. sebiferum are not browsed by cattle; they contain constituents such as gallic acid, astragalin (active against lymphatic leukemia cells), (-)-laliolide, kaempferol, quercetin, β-sitosterol glycoside, and a phenolic glycoside with antihypertensive activity.
T. sebiferum contains hydrolyzable tannins, including geraniin (the main type, even present in callus cultures) and ellagic acid. The stem bark contains various triterpenoids and 3,4-di-O-methyl ellagic acid. The bark contains a sticky milky-white sap which may act as a skin irritant and purgative. The bark of the roots contains xyloglucosides of xanthoxylin, moretenone, moretenol, xanthoxylin, and sitosterol-β-D-glucoside. As a fuel extender, the properties of vegetable tallow and stillingia oil were comparable to those of diesel fuel. Diesel fuel extended with 50% vegetable tallow and stillingia oil was used successfully in diesel engines in short-term tests. The power output, fuel consumption rates and thermal efficiencies of the engine were within 7% of the values obtained using pure diesel fuel. The wood of T. sebiferum is hard, close grained and nearly white with a density of about 500 kg/m3at 15% moisture content. The weight of 1000 seeds is about 150 g.
Monoecious, deciduous shrub or tree, up to 8(-15) m tall. Stem often gnarled (in its natural state), bark whitish-grey with vertical cracks, when wounded exuding a white juice. Leaves alternate; stipules ovate to triangular, up to 2 mm long; petiole 2.5-4 cm long, at apex (or base of blade) ending in a pair of conspicuous glands; blade broadly ovate to orbicular, 3.5-8.5 cm × 2.5-9 cm, less than twice as long as wide, base rounded, margin entire, apex acuminate, secondary veins 8-10 pairs arching and joined towards the margin, smaller veins closely and distinctly reticulate, turning orange to scarlet in autumn, falling early in the cold season. Inflorescence a terminal or upper axillary thyrse, 7-14 cm long, yellowish, basal part with female, upper part with male cymules; bracts and bracteoles present, often with a pair of glands at base, petals absent; female cymules 1-flowered, only 2-6 per thyrse; female flower with pedicel up to 1 cm long, calyx 3-lobed, ovary 3-locular, style ending in 3 stigmas; male cymules 3-8-flowered; male flower with pedicel longer than 2 mm, calyx lobes 3-6, stamens 2-3 with filaments longer than anthers. Fruit a dry, 3-seeded (3-lobed or grooved), subglobose schizocarp, 1-1.5 cm in diameter, opening regularly and nearly simultaneously septicidally and loculicidally; stalk up to 1.5 cm long; mericarps with persistent columella. Seeds 3, attached to the central columella for a considerable time after ripening, subglobose to flattened ovoid, 6-10 mm × 4-6 mm × 5-8 mm, covered with a white, waxy, persistent sarcotesta; seedcoat (shell) hard, brittle, brown.
Growth and development
Under favourable conditions T. sebiferum is a fast grower: in its early years (until 8-10 years) it grows about 1 m per year; after 20 years, it is 8-13 m tall with a stem diameter of 30-40 cm. Flowering starts 3-4 years after planting and the flowers are very fragrant and freely visited by bees and other insects. The fruits take 3-4 months to ripen. In seasonal climates, the tree is very ornamental with reddish inflorescences with green-yellow flowers in spring, conspicuous white seeds that remain long on the tree a few months later, and with leaves turning a brilliant red in autumn. In China, trees are long-lived and said to become several hundred years old. To run wild in areas where it has been introduced, it needs a fair amount of annual rainfall or a permanently moist soil. In Florida and Louisiana (United States), where such conditions occur, it has been declared a noxious weed.
Other botanical information
In the taxonomic literature, Chinese tallow tree has long been named Sapium sebiferum , and was classified in section Triadica of the genus Sapium Jacq. in the tribe Hippomaneae of the family Euphorbiaceae . The Hippomaneae comprises about 30 genera now, with about 300 species. The genus delimitation in Hippomaneae is still in debate and the genus Triadica Lour. is not well known. Triadica comprises only 2 species at present, but the number might increase, probably to 4.
T. sebiferum has often been confused with species of Homalanthus A. Juss., particularly H. populneus (Geiseler) Pax. Homalanthus can be distinguished from Triadica by its 3-flowered staminate cymules (3-8 in Triadica ), its small 2-carpelled fruits with thin fleshy pericarp (3-carpelled and dry in Triadica ) and seeds with a reddish sarcotesta (white in Triadica ).
The second Triadica species is T. cochinchinensis Lour., occurring all over South-East Asia, northern India and eastern China, used primarily as a medicinal plant, but also as timber and as forage. Its sarcotesta contains little palmitic acid and is not used. It can be distinguished from T. sebiferum by its leaves that are elliptical and more than twice as long as wide.
Although T. sebiferum has naturalized in the vicinity of Jakarta, several attempts to establish the tree in Singapore failed.
The seeds (kernels) of the related Shirakiopsis indica (Willd.) Esser (synonyms: Excoecaria indica (Willd.) Muell. Arg., Sapium indicum Willd.) also produce an edible oil and the tree is sometimes called "Borneo tallow tree".
T. sebiferum occurs in subtropical to warm temperate climates. It can withstand a few degrees of frost and tolerates a wide range of soils within pH range of 5-8. It thrives in waterlogged and moist locations and survives salt-water flooding. Optimum conditions are an annual rainfall of 1500-3000 mm, temperatures of 15-30°C, elevations from sea level up to 800 m on well-drained clayey-peat soils. In the United States, it survives in unburned grassland, in disturbed and undisturbed upland and wetland sites. It is shade tolerant and grows under closed canopies. In India, it can be found on gravelly soils in ravines.
Propagation and planting
T. sebiferum can be easily propagated by seed (most common), cuttings, layering, top-grafting and root suckers (which are formed abundantly). Seeds are sown directly in the field, 3-4 per hole and 5 m distance between holes, giving 400 trees/ha. Seeds are usually planted in early spring or late autumn. Large seeds have the best germination rate (90%). In India, soaking seed in concentrated sulphuric acid for 10 minutes promoted germination effectively, while plants grown from suckers showed better growth than seedlings. An in vitro technique based on axillary bud proliferation has been developed.
In plantations of T. sebiferum , trees should be trimmed and kept to a convenient size for hand harvesting.
Diseases and pests
T. sebiferum has no serious diseases or pests. However, fungi such as Cercospora stillingiae and Clitocybe tabescens , and the plant parasite Dendrophthoe falcata L.f. ( Loranthaceae ) are known to attack it. In India, the tree is sometimes defoliated by larvae of the moth Achaea janata (synonym Ophiusa melicerta ). The rootknot nematode Meloidogyne javanica has also been recorded as causing damage. Birds can inflict damage because they like the seeds.
T. sebiferum starts bearing fruit 3-8 years after planting, although in Hawaii trees fruited already 18 months after sowing. In China, harvesting is done during September-November when fruit bunches have turned brownish. Where T. sebiferum is not cultivated, large-scale harvesting is only carried out in areas where the trees are abundant. Fruits are harvested with a sharp, crescent knife attached to a long pole or by hand by lopping off the ends of the branches, which has the effect of a severe pruning. Because T. sebiferum coppices very well, it is a suitable tree for biomass production.
Annual seed yields per tree are estimated at 8-12 kg when 7-8 years old and 30-35 kg when fully grown. With 400 trees/ha, annual seed yields may reach 12 -14 t, giving 2-2.5 t vegetable tallow, 2-2.5 t stillingia oil, 4.5 t husk, 1 t seedcoat, 1.5 t protein-rich presscake. In the United States, T. sebiferum showed itself to be an interesting woody biomass supplier on poorly drained and saline soils in the hot southern coast region, yielding 6-10 t/ha dry biomass annually.
Handling after harvest
Harvested fruits of T. sebiferum are dried on mats in the sun, they turn black and split open so that seeds can easily be removed by hand, by threshing or by treading under foot. Another way of loosening seeds is by gently pounding the capsules. The dried husks of the fruits are commonly used in China as fuel for the fires needed to extract the tallow. By heating the seed with boiling water or steam, the fat from the sarcotesta melts and forms the Chinese tallow; after that the seeds are crushed and pressed to collect the drying oil from the cotyledons. Sometimes seeds with sarcotesta are crushed and pressed and a mixture of vegetable tallow and stillingia oil is produced which has a much reduced commercial value. The sarcotesta can also be removed by passing the seed between fluted rollers that break it off without crushing the seed. In India, solvent extraction of the seeds for tallow and stillingia oil gave 50% more produce.
T. sebiferum is widespread and easily runs wild so there is no danger as yet of genetic erosion or extinction. Germplasm collections, however, are small or non-existent.
In Taiwan, there are more than 100 cultivars of T. sebiferum ; two important cultivars are "Eagle-claw" and "Grape", which differ in fruit form and maturation period. In India, T. sebiferum easily hybridizes with the indigenous species Sapium eugeniaefolium Ham. The hybrid is more vigorous, possibly endangering the future of S. eugeniaefolium in some areas.
T. sebiferum is a useful tree since it produces fat, oil and biomass and is able to grow in a wide range of environments unsuited for many other plant resources. In cooler areas of South-East Asia with marginal, poorly drained soils, it is worthwhile investigating the possibilities for its cultivation. It does not require much care or input. However, to be economically profitable, the production of its various products, especially the oil, must be optimized. Research is needed to develop an efficient, low-cost extraction method to enhance the oil yield which is the crop's most important product.
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B.E. Umali & P.C.M. Jansen