Hevea is a genus of flowering plants in the spurge family, Euphorbiaceae, with about ten members. It is also one of many names used commercially for the wood of the most economically important rubber tree, H. brasiliensis. The genus is native to tropical South America but is widely cultivated in other tropical countries and naturalized in several of them. It was first described in 1775.
Characteristics
French botanist and explorer Jean Baptiste Christophore Fusée Aublet first described Hevea as a genus in 1775. H. brasiliensis and H. guianensis are large trees, often reaching more than in height. Most of the other members of the genus are small to medium trees, and H. camporum is a shrub of around . Trees in this genus are either deciduous or evergreen. Certain species, namely H. benthamiana, H. brasiliensis and H. microphylla, bear "winter shoots", stubby side shoots with short internodes, scale leaves on the stem and larger leaves near the tip; on these, the leaves are shed leaving the tree bare before new shoots develop.
The most widespread species is H. guianensis which occurs over the whole range of the genus. In this area where there are variations in soil and topography and the rainforest experiences conditions of all-year-round humidity, the genus Hevea has been undergoing a high degree of speciation. The high humidity encourages the growth of fungal leaf diseases, and the species that are deciduous avoid immediate transfer of fungal spores from old leaves onto new growth.
Habitat
Each species has its own habitat requirements; H. brasiliensis grows on well-drained soils but tolerates light flooding; H. guianensis, H. pauciflora and H. rigidifolia grow in well-drained soil, on high river banks and on slopes; and H. camporum grows on savannahs. Other species such as H. benthamiana, H. microphylla and H. spruceana need wetter conditions in locations subject to seasonal flooding for several months each year, and H. nitida grows both in periodically inundated swamps and in drier locations such as rocky hillsides well above the flood level.
Historical Uses
Indigenous groups in Mesoamerica collected the sap through tapping. They formed rubber bouncing balls for games and also used dried sap to waterproof their clothing.
European Discovery
The initial discovery is believed to be by Christopher Columbus in the 15th-16th century, through accounts of him returning with a rubber ball. The curiosity came from the soft, sticky texture when warm and hard, brittle texture when soft. There was no commercial development until the 19th century, beyond small-scale waterproofing and erasers.
Pneumatic tires
In 1839, Charles Goodyear accidentally spilled a combination of rubber and sulfur on a hot stove. Through vulcanization the rubber maintained its elasticity when cold and was no longer sticky while hot. From this discovery, in 1887 pneumatic tires were created for both bicycles and cars, leading to an increase in rubber demand.
Botanical Piracy
With the development of the pneumatic tire industry, trees were being tapped at too fast a rate to maintain. In response, Brazil banned the trading of Hevea trees and seeds to protect its primary export. However, in 1876 Henry Wickham, a British envoy from Kew Gardens, stole over 70,000 seeds which were shipped across the world. Only 12 seeds germinated and survived in Asia, where China and India were able to develop hevea plantations and dominate the rubber industry.
Species
The following species are recognised: