It is a large tree in the banyan group of figs, growing to 30–40 metres (98–130 ft) (rarely up to 60 metres / 200 feet) tall, with a stout trunk up to 2 metres (6.6 ft) diameter. The trunk develops aerial and buttressing roots to anchor it in the soil and help support heavy branches. It has broad shiny oval leaves 10–35 centimetres (3.9–14 in) long and 5–15 centimetres (2.0–5.9 in) broad; leaf size is largest on young plants (occasionally to 45 centimetres / 18 inches long), much smaller on old trees (typically 10 centimetres / 3.9 inches long). The leaves develop inside a sheath at the apical meristem, which grows larger as the new leaf develops. When it is mature, it unfurls and the sheath drops off the plant. Inside the new leaf, another immature leaf is waiting to develop.
As with other members of the genus Ficus, the flowers require a particular species of fig wasp to pollinate it in a co-evolved relationship. Because of this relationship, the rubber plant does not produce highly colourful or fragrant flowers to attract other pollinators. The fruit is a small yellow-green oval fig 1 centimetre (0.39 in) long, barely edible; it will only contain viable seed where the relevant fig wasp species is present.
Cultivation and uses
Ficus elastica is grown around the world as an ornamental plant, outside in frost-free climates from the tropical to the Mediterranean and inside in colder climates as a houseplant. Although it is grown in Hawaii, the species of fig wasp required to allow it to spread naturally is not present there.
In cultivation, it prefers bright sunlight but not hot temperatures. It has a high tolerance for drought, but prefers humidity and thrives in wet, tropical conditions. Ornamental hybrids (such as Robusta) have been derived from Ficus elastica with broader, stiffer and more upright leaves than the wild form. Many such hybrids exist, often with variegated leaves.
Most cultivated plants are produced by asexual propagation. This can be done by planting cuttings or air layering. The latter method requires the propagator to cut a slit in the plant's stem. The wound, which oozes with the plant's latex, is packed with rooting hormone and wrapped tightly with moist sphagnum moss. The whole structure is wrapped in plastic and left for a few months. When it is unwrapped, new roots have developed from the plant's auxiliary buds. The stem is severed and the new plant is potted on its own.
Ficus elastica yields a milky white latex, a chemical compound separate from its sap and carried and stored in different cells. This latex was formerly used to make rubber, but it should not be confused with the Pará rubber tree, the main commercial source of latex for rubber making. This latex is also an irritant to the eyes and skin and can be fatal if taken internally.
Illustration from Köhler's Medicinal Plants (1887)
Stem of Ficus elastica
Ficus elastica near the roadside in Savusavu, Fiji, showing the effects of constant pruning on the growth form.
A huge Ficus elastica tree in Ghana showing the aerial roots.
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