Hevea brasiliensis

Hevea brasiliensis is a flowering plant in the spurge family, known as Euphorbiaceae. It is most commonly called the rubber tree or rubber plant. This species is the most economically important member of the genus Hevea. This importance comes from its milky latex, which is the primary source of natural rubber.

While it is originally native to the Amazon basin, it is now grown in many tropical regions worldwide. It is a tall, deciduous tree that can reach great heights in the wild.

The tree produces latex through a specific biological mechanism. White or yellow latex is stored in specialized latex vessels located in the bark. These vessels are positioned mostly outside the phloem, which is the tissue that transports nutrients. The vessels form a right-handed helix that spirals up the trunk. This spiral maintains an angle of about 30 degrees from the horizontal. These vessels can grow as high as 30 meters up the tree.

To harvest this resource, workers perform a process called rubber tapping. Harvesters make precise incisions across the latex vessels in the bark. These cuts must be deep enough to reach the vessels but shallow enough to avoid harming the tree's growth. Once the vessels are cut, the latex flows out and is collected in small buckets.

This process requires patience, as it takes between seven and ten years for a tree to deliver its first harvest. In commercial plantations, trees are often smaller than wild trees. This is because tapping the latex restricts their growth, and trees are usually cut down after 30 years. This happens because latex production declines as the trees age.

The history of the rubber tree is marked by periods of great wealth and sudden change. Native people in the Amazon used the tree long before modern industry arrived. In Mesoamerica, the Olmec people used similar latex-producing trees as early as 3,600 years ago. They used the rubber to create balls for their traditional ballgames. Later, the discovery of the vulcanization procedure in 1839 triggered a massive rubber boom. Between 1840 and 1913, this boom enriched South American cities like Belém, Santarém, Manaus, and Iquitos.

Global rubber production changed forever due to a major smuggling operation. In 1873, early attempts to grow the tree outside Brazil failed. However, in 1875, Henry Wickham smuggled approximately 70,000 seeds to the Royal Botanic Gardens, Kew. About 4% of these seeds germinated successfully. In 1876, about 2,000 seedlings were sent to Ceylon, while 22 seedlings were sent to Singapore.

This allowed rubber to be extensively grown in British colonies. By 1898, large plantations were established in Malaya, using imported Chinese field workers.

Today, the center of rubber production has shifted to South and Southeast Asia. In 2011, the top producing countries included Thailand, Indonesia, Malaysia, India, and Vietnam.

These trees require a tropical or subtropical climate with at least 2,000 mm of annual rainfall. They cannot tolerate frost, as a single frost can be disastrous. Frost can cause the refined rubber to become brittle and break. Production in the Amazon declined in the early 20th century due to a disease called South American leaf blight. This blight is caused by the fungus Pseudocercospora ulei. Because many Asian clones are susceptible to this fungus, experts worry about future industry stability.

The tree also uses complex chemistry to defend itself. Hevea brasiliensis produces cyanogenic glycosides, or CGs, which are concentrated in the seeds.

These chemicals act as a defense against many attackers. The tree can recycle the carbon and nitrogen from these compounds for growth or latex production. Interestingly, the tree can suffer more from the leaf blight if it produces more of these defensive chemicals. This is because the cyanide may stop the tree from producing other necessary defenses. This complex relationship between the plant and its environment shapes how the rubber tree survives and grows.