Common Name: Rubber Plant

General Information

Rubber plant is a large, evergreen tree, growing up to 55 metres tall with abundant aerial roots from the trunk and the main branches which do not thicken to form 'pillar roots'[]. The plant often begins life as an epiphyte, growing in the branch of another tree; as it grows older it sends down aerial roots which, when they reach the ground quickly form roots and become much thicker and more vigorous. They supply nutrients to the fig, allowing it to grow faster than the host tree. The aerial roots gradually encircle the host tree, preventing its main trunk from expanding, whilst at the same time the foliage smothers the foliage of the host. Eventually the host dies, leaving the fig to carry on growing without competition[].
The tree is harvested from the wild for local use as a food, medicine and source of latex. It was at one time cultivated in plantations in Asia and west Africa for the production of latex[]. It is grown as an ornamental tree in all tropical regions and is a very popular indoor plant all round the world[]. The latex had become a trade commodity by the middle of the 19th century, when prices rose for a product that had previously only been used locally. However, interest in the crop waned in favour of Hevea brasiliensis (the Brazilian rubber tree) which could produce higher yields of higher quality latex. Most trade in the latex of this plant had ceased by 1920[].

Known Hazards

None known

Botanical References

Range

E. Asia - India, Bhutan, Nepal, Myanmar, Malaysia, Indonesia.

Habitat

Hill forest, particularly on cliffs and limestone hills[].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Tree
Height	50.00 m
Pollinators	Wasps
Cultivation Status	Cultivated, Ornamental, Wild

Cultivation Details

A plant of the dry to moist tropics, where it is found at elevations up to 1,650 metres. It grows best in areas where annual daytime temperatures are within the range 20 - 30°c, but can tolerate 10 - 36°c[]. It can be killed by temperatures of -1°c or lower[]. It prefers a mean annual rainfall in the range 600 - 1,000mm, but tolerates 300 - 2,800mm[].
Prefers a sunny position[, ]. Succeeds in most well-drained soils of moderate fertility[, ]. Prefers a pH in the range 5.5 - 7.5, tolerating 5 - 8.3[].
Ficus 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[].
Young specimens in Java are reported to be epiphytic. The root system of Ficus elastica is shallow and dense, making mixed plantation or intercropping systems impossible. Roots may spread over a distance of 40 metres, as reported for India[].
The yield of individual trees in plantations of Ficus 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 metres in diameter yielded 15 kg rubber; the average yields in three consecutive years of 50 wild trees measuring 34 metres 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[].
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 Ficus elastica is Blastophaga clavigera, known from India. In Ficus 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.
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 Ficus elastica is Blastophaga clavigera, known from India. In Ficus 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[].

Edible Uses

Young leaves are eaten as vegetable[]. The very young leaf tips, harvested before the leaves have expanded, are eaten as a salad[].

Medicinal

A decoction of the aerial rootlets is used as a vulnerary[].

The latex has been successfully used to treat five cases of trichuriasis[].

Other Uses

A latex is obtained from the bark of the stem and larger branches[, ]. This 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[].
Traditionally, the latex is used to line baskets of split rattan, to make them watertight[], and has sundry other applications[].

The rubber made from this plant 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 of wild as well as planted trees can be 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, , 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 'scrap' from Ficus 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[].

The latex showed toxicity to the juveniles of the nematode Meloidogyne javanica[].

The fibrous bark has been used for the manufacture of clothes and ropes[].

The wood is of poor quality, but is occasionally applied for boards, posts, boats and fuel[].

Propagation

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 metres 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[].

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