Teak is a hardwood tree that grows in rainforest climates. Because the tree has evolved to survive the harsh heat and moisture of the rainforest, the wood is virtually rot proof. Additionally the straight, close grain of teak wood is ideal for furniture.
Teak wood is ideal for furniture, but the tree is very slow growing, so it is difficult to manage a forest by planting new trees to supply future demand. Most teak was harvested by clear cutting rain forests in Thailand and Burma, until that was banned. Teak is still illegally poached from those countries today. The U.S. Trade Department has banned the importation of teak harvested from Burma because the teak trade finances the military dictatorship of that country.
The best teak alternative is plantation raised teak. Plantation raised teak has all the properties of teak with none of the environmental damage. The Dutch colonists planted teak plantations on the island of Java as early as 1816. Today, these plantations are owned and operated by the government of Indonesia to ensure a long-term supply of teak wood. The Pacific coast of Mexico also has teak plantations. Sustainable, plantation raised teak is expensive, so other woods are used today for outdoor furniture.
Ipê is a South American species of tree. Its wood is hard and dense to resist rot, but the grain is wavy. Because of the wavy grain, Ipê is better for decking than furniture. Eucalyptus wood is a good alternative to teak for furniture building, although it needs to be properly cured before use otherwise it will chip and crack.