Ficus elastica (PROSEA)
Ficus elastica Roxb.
- Protologue: Hort. Bengal.: 65 (1814).
- Family: Moraceae
- Chromosome number: 2n= 26
- Visiania elastica (Roxb.) Gasp. (1844),
- Urostigma elasticum (Roxb.) Miq. (1847).
- India rubber tree (En).
- Arbre à caoutchouc (Fr)
- Indonesia: rambung (eastern Sumatra), kajai (Padang), (ki) karet (Sundanese)
- Malaysia: bunoh seteroh (Kelantan)
- Burma (Myanmar): bedi
- Thailand: yaang lop, yaang india (central), lung (northern)
- Vietnam: cây đa.
Origin and geographic distribution
F. elastica is found naturally in north-eastern India (Sikkim, Assam), Burma (Myanmar), northern Peninsular Malaysia, and in Indonesia (Sumatra, Java). It is cultivated and introduced worldwide; outside the tropics it is grown indoors and in greenhouses.
The latex from the bark of the stem and larger branches of F. elastica contains rubber, which can be used for all applications of natural rubber, such as tyres, rubber components for cars and machines and consumer products such as footwear, sport goods, toys and gloves. Centuries ago, the latex was used to line baskets of split rattan, to make them watertight. In the late 19th and early 20th Centuries plantations were established, mainly in Sumatra, Java and Peninsular Malaysia, but India rubber was soon eclipsed by para rubber (Hevea brasiliensis (Willd. ex Juss.) Müll.Arg. F. elastica is presently a very common ornamental or shade tree which is also cultivated as a foliage pot plant.
The very young leaf tips have been eaten as a vegetable in Java. The fibrous bark has been used for the manufacture of clothes and ropes. The wood is of poor quality and occasionally applied for boards, posts, boats and fuel.
Production and international trade
In West Java, the latex of F. elastica became a trade commodity by 1850, when prices rose for a product that had previously only been used locally. In the period 1873-1896 the mean annual exports were: 393 t from Bangladesh, 187 t from Burma (Myanmar), 189 t from Assam (India), 30 t from Singapore, 28 t from Sumatra and 17 t from Java. After this period trade declined, ceasing in about 1920.
The latex has a specific gravity of 0.96-1.00 and contains (10-)30-40(-58)% rubber with relatively large rubber particles in the latex compared with other latexes. The resin content of the latex varies widely, with estimates ranging from 3% to 25%. Latex from older trees contains less resin, as does the older tissue in a plant: the latex from the top of a plant 2.3 m tall contained 25% resin while latex collected from its base contained 18% resin. The resin content of the latex of trees grown at higher altitudes is higher: latex from trees grown at 45 m altitude contained 3% resin and that from trees growing at 750 m altitude 22% resin. The rubber made from F. elastica contains 4-20% resin, which hardens over time and decreases the rubber's elasticity. The rubber has relatively short chains of polyisoprenes of low molecular weight: 78 000. It is soluble in cajeput oil (Melaleuca cajuputi Powell). The rubber is hypoallergenic to individuals allergic to the proteins found in Hevea brasiliensis rubber products. The latex showed toxicity to the juveniles of the nematode Meloidogyne javanica.
- A large, evergreen, strangling tree, up to 55 m tall with abundant aerial roots from the trunk and the main branches which do not thicken to form "pillar roots", bark surface smooth, inner bark pale pink producing white latex; twigs glabrous.
- Leaves arranged spirally, simple; stipules lanceolate and flaccid, connate into an accrescent, narrow, membranous, bright red, long-acuminate cap, 7-35 cm long, largest on lower branches; petiole 2-5 cm long, red when young; blade oblong to elliptical, usually 10-15 cm × 4-7.5 cm, up to 40 cm × 22 cm on lower branches and in saplings, dark green, glabrous, leathery, base cuneate to almost rounded, margin entire, apex shortly acuminate, up to 25 mm long on lower branches, primary vein red when young, with 13-26 pairs of well-developed parallel secondary veins, with intramarginal veins, upper leaf surface with abundant cystoliths, stomata deeply sunken.
- Inflorescence a fig (syconium), axillary, in pairs, sometimes solitary; peduncle 1-3 mm long, finely puberulous; basal bracts 3, 3 mm long, falling off very early with the stipules and leaving an annular scar.
- Flowers unisexual; male flowers dispersed, with short pedicel, tepals (3-)4, free, eventually spreading, stamen 1, anther 4-celled, dehiscing longitudinally; gall flowers sessile or with short pedicel; female flowers sessile, tepals 4, free, ovary unilocular, emergent, with a single ovule, style single, subterminal, stigma simple, subcapitate.
- Infructescence a fig, shortly ellipsoidal, 9-12 mm × 8-9 mm, yellow when ripe; individual fruit a drupelet.
- Seedling with epigeal germination; cotyledons emergent, cotyledons and first pair of leaves appear simultaneously; hypocotyl elongated; first pair of leaves with coarsely-crenate margin with fine punctuations which disappear in older leaves, all leaves arranged spirally.
Growth and development
The symbiotic relation of Ficus spp. with specialized wasps is well-known. Figs can only be pollinated by female agaonid wasps (Hymenoptera, Chalcidoidea, Agaonidae). These wasps are highly species-specific; the fig-wasp associated with F. elastica is Blastophaga clavigera, known from India. In F. elastica the wasps arrive when female flowers are receptive. They enter the fig via the osteole, a bract-covered apical pore. Once inside they pollinate the female flowers and deposit their eggs in the ovaries. As style length varies greatly within these figs and because the wasp can only reach the ovary of short-styled flowers, only some of the flowers obtain an egg, while in others the seed develops. Male and female wasps emerge after a few weeks, and mate within the fig. The females then emerge from the fig and, in so doing pick up pollen from the newly mature anthers of male flowers. Figs on a single tree mature at the same time, while different trees of the same species flower out of synchrony, thus inducing cross-pollination. F. elastica seedlings develop root nodules containing 95% water, which act as a water reservoir. This most probably helps the seedlings to survive the initial epiphytic phase. During this phase the plant sends down thin aerial roots which only thicken after they have reached the ground. In Java, F. elastica flowers throughout the year. In Luzon, the Philippines, it flowers in January-March. Young specimens in Java are reported to be epiphytic. The root system of F. elastica is shallow and dense, making mixed plantation or intercropping systems impossible. Roots may anastomose over a distance of 40 m, as reported for India.
Other botanical information
Roxburgh's publication of the name F. elastica in 1814 in the catalogue of the Hortus Bengalensis is often considered as a nomen nudem which was validated 5 years later by Hornemann. The publication of the name in 1814 is, however, not a nomen nudem because Roxburgh added "LT", a code for "Large Tree", "HS", a code for flowering in the "Hot Season", "RS", a code for fruiting in the "Rainy Season" and he states that the fruit is solitary or paired, that the tree abounds in rubber, that its Bengal name is "kusmeer" and that the tree arrived in the garden in 1810, brought by a Mr. M.R. Smith.
Because F. elastica is easily propagated by cuttings, it often escapes from cultivation. Its true wild status in Malesia is questioned, because fertile seed and the wasp have never been found there. Based on colour, size and odour numerous subclassifications have been made without much practical value. Many cultivars have been developed for ornamental indoor plants.
More than ten cultivars of F. elastica are distinguished, all used as foliage pot plants. The best known are: "Decora" with thick, hard and shiny green leaves, "Doescheri" with pinkish petioles, grey-green and creamy yellow leaves with green margins, "Belgaplant" with variegated leaves, "Robusta" with large rounded leaves to 45 cm long, "Tricolor" with yellowish to cream-coloured leaves, and "Variegata" with yellow markings and a yellow margin.
F. elastica occurs naturally in areas with temperatures of 8-33°C and an annual precipitation of 1750-3750 mm without a marked dry season. It does not tolerate waterlogging. It is found scattered in the lowland rain forest of southern West Java and in hill forest, particularly on cliffs and limestone hills. Plantations need full light for optimal development.
Propagation and planting
F. elastica can be propagated by seed, cuttings and air layering. Seed viability is 20-50% and apparently does not decrease over the first three months of storage. After the seeds have been cleaned from the surrounding pulp they are sown under shade; the first seedlings appear 2 weeks later. Seeds taken from bird or bat excrement are reported to germinate more readily. After the first 2 pairs of leaves have developed, the seedlings are pricked out and placed in trays under shade. The seedlings are transferred to beds when they are several cm tall at a spacing of 25-40 cm. Once they are well established the shade is gradually removed and eventually the seedlings are in full sunlight. Seedlings can be planted out in the field when they are 35-40 cm tall, which is only after about one year, as initial growth is slow. In India, it was common practice to plant out when 3 m tall. For vegetative propagation the highest-yielding mother trees are chosen, which is important as there is a large individual difference in latex yield. Branches cut at a slant can be planted directly, provided the wood of the cutting is not too young. Initially, planted cuttings need support, to prevent root damage from wind rock. Air layering is also very successful; layers can be severed from the mother plant after only 40 days. In the heyday of F. elastica plantation establishment, wildlings were collected and traded in Sumatra. The recommendations for the spacing in F. elastica plantations varied widely, from 2 to 12 m apart. A spacing of 10 m seemed favoured in Indonesia, provided weeds could be controlled. Rooted air-layers have also been "planted" on trees in the forks of branches, but this practice has never been common. Experimentally, F. elastica has been propagated by inserting in-vitro shoots directly into non-sterile sand to induce rooting, thus eliminating the in-vitro rooting step. Plants from unrooted tissue culture are used for pot plant production.
In plantations common management practices such as weed control and protection from livestock were practised. Moreover, the thin aerial roots were regularly trimmed, so that the stem could easily be reached for tapping. Plantations where initial spacing had been dense (e.g. 4 m × 4 m) to reduce weed growth were subsequently thinned.
Diseases and pests
A common disease of F. elastica pot plants is anthracnose caused by the fungus Glomerella cingulata. Anthracnose develops pale rose-coloured pustules, usually scattered along the veins. Any wound or breaking of leaves or accumulation of water on the leaves for considerable periods will favour infection. Twig blight and canker caused by Fusarium lateritium are other diseases of F. elastica pot plants.
As the latex of F. elastica is not harvested at present, the harvesting techniques described here are those used a century ago. The latex of wild as well as planted trees is collected by tapping the bark, generally only of the stem and larger branches, though root bark may also be tapped. It is best to harvest when the air humidity is high, as drier conditions cause the latex to coagulate too fast and rain reduces the rubber content of the exudate. Traditionally the bark was cut with a knife or small axe, later incisions were made with a gouge to better control the depth of cutting and to limit the wounding of the cambium. In the bark the laticifers are found closest to the cambium in a fibrous tissue which is difficult to cut. If the incision is not deep enough, the tissue containing most laticifers is not tapped and yield is low. A deep incision damages the cambium and hence influences the vitality of the tree. A V-shaped gouge can also be used to make horizontal incisions up to 5 cm wide and some 20 cm long, the length never exceeding half the circumference of the tree. These cuts are about 40 cm apart and on opposite sides of the tree. A herringbone system has also been applied, in which a central vertical channel transports the latex from grooves made at an angle of 45° with the vertical to a container driven into the bark of the tree. Inside the inclined grooves the fibres are punctured or cut at intervals of 2-3 cm, to tap the laticifers closest to the cambium. This, however, also punctures or cuts the cambium layer. An advantage of the herringbone system is that the latex is collected as a fluid and is of better quality than the "scrap" collected from the horizontal incisions or from underneath the tree. The latex drips from the horizontal incisions for about 2-3 minutes and is collected on a mat or on leaves placed underneath the tree. The coagulated latex is collected 2-3 days later; when stripped off the incision a milky residue oozes from the wound, but this liquid contains no rubber. A well-developed planted tree can be tapped after 6-7 years, but with increasing age (and circumference of the tree) when the first tapping is done, both yield as well as rubber content of the latex increase.
There has been much debate and experimenting on the frequency of tapping. In this respect it is important that the latex extracted is not replaced and that there is no anastomosis between the laticifers, so only the latex from the immediate vicinity of the tapping wound exudes. This is why consecutive tappings, whether every day or once a year for three years, have shown a marked decrease in yield. Yields in g/tree from a tapping trial with 55 trees in Bogor for four harvests at intervals of 2, 3, and 4 years were 238 g, 67 g, 70 g and 320 g. This suggests that it takes four years before the laticifers are reconstituted. Provided the tree will survive, it is therefore more rational to extract the maximum amount of latex at once, rather than tapping trees several times over a period of few years.
The yield of individual trees in plantations of F. elastica can vary very widely, the highest attains 30 times more than the lowest. The yield of the first harvest is directly influenced by the circumference of the tree and the horizontal length of the incision. A tree of 1.8 m in diameter yielded 15 kg rubber; the average yields in three consecutive years of 50 wild trees measuring 34 m tall and 5.7 m in diameter (aerial roots included) were 4, 1.9 and 0.4 kg/tree respectively. The average annual yield of 55 trees in Bogor Botanical Gardens tapped four times at the age of 8 to 17 years is only 41 g/tree. It has been reported that the first yield of a tapped aerial root with a diameter of 15 cm yielded 9.3 kg of rubber, but this exceptionally high yield was never confirmed by other measurements.
In Indonesia the latex product is known as "getah munding", in Malaysia as "getah rambong", "getah karet" or "getah achin".
Handling after harvest
The "scrap" from F. elastica is sorted by hand and cleaned. The latex is difficult to coagulate: neither heating nor adding organic or mineral acids, even concentrated sulphuric acid, or alkali, will cause it to coagulate. Instead, it must be beaten and kneaded, and alcohol must be added. This yields a superior product which does not become sticky with time. Ammonia and tannin have been used as coagulants in Peninsular Malaysia. The "scrap" and the coagulated latex are pressed into blocks, cakes or sheets before being traded.
No germplasm collections of F. elastica as an exudate are known to exist.
Superior mother trees of F. elastica with high latex yields have been selected to provide cuttings and air layers, but no breeding programmes as such have been developed. Several cultivars have been developed for the production of foliage pot plants.
F. elastica is an important ornamental tree in South-East Asia. Its use for producing India rubber is now negligible, because of the higher yield and better quality of para rubber. However, India rubber is hypoallergenic to individuals allergic to some proteins contained in Hevea brasiliensis rubber and may become important because of this special property.
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- Coventry, E.M., 1906. Ficus elastica: its natural growth and artificial propagation. India Forest Bulletin 4. Office of the Superintendent of the Government Publishing, Calcutta, India. 35 pp.
- Heyl, C.J.W., 1901. Vermenigvuldiging der voornaamste caoutchouc en gutta-percha leverende planten [Propagation of the most important rubber and gutta-percha-yielding plants]. Teysmannia 11: 167-172.
- Salverda, A.T., 1908. Verkorte inhoud van de voordracht gehouden door den houtvester Salverda over kaoetsjoek, op de algemene houtvestersvergadering te Djocja [Abstract of the lecture on rubber, by the Forest District Officer Salverda, at the general meeting of Forest District Officers in Yogya]. Tectona 1: 3-7.
- van Gelder, A., 1911. Het een en ander over winnen en bereiden van caoutchouc van de Ficus elastica [Some information on the collection and preparation of rubber from Ficus elastica]. Tectona 4: 478-489.
- van Romburgh, P., 1899. Over caoutchouc-leverende planten. 4. Ficus elastica Roxb. of Urostigma elasticum Miq. [On rubber-yielding plants. 4. Ficus elastica Roxb. or Urostigma elasticum Miq.]. Teysmannia 9: 519-534.
- van Romburgh, P., 1900. Caoutchouc en getah-pertja in Nederlandsch-Indië [Rubber and gutta-percha in the Dutch East Indies]. Mededeelingen uit ‘s Lands Plantentuin, Buitenzorg 39: 40-61.
- van Romburgh, P., 1901. Het kweeken van Ficus elastica uit zaad [Propagation of Ficus elastica by seed]. Teysmannia 11: 351-353.
- Vernet, G., 1910. Etude générale sur le Ficus elastica Roxb. [General study of Ficus elastica Roxb.]. Paris, France. 31 pp.