Rubber (cis polyisoprene) is a by-product of the cell metabolism of many species of plants, mostly belonging to the family Euphorbiaceae. Most rubber-containing plants are native to the tropics: Hevea spp., Castilla spp. and Manihot spp. in Tropical America, Funtumia elastica and Landolphia spp, in Africa, Ficus elastica in Asia. There are also some rubber-bearing species of Compositae: Parthenium argentatum (Central America), Taraxacum (USSR), Solidago spp. (USA).

With the exception of Parthenium (guayule), which remains a small-scale source for rubber in Mexico (and in Arizona), the only significant commercial source of natural rubber is Hevea brasiliensis, a forest tree which is indigenous to the tropical rain forests of Central and South America. In this and similar species, the rubber exists within the tree in the form of latex, a colloidal suspension of rubber particles. Despite speculation, the function of latex in the tree remains unknown (Webster and Faardekooper, 1989).

In Brazil and other Latin American countries Hevea benthemiana including Hevea brasiliensis crossings are an important source of relatively SALB-free sources of rubber.

Funtumia elastica is the rubber plant which is widely used as a decorative indoor plant in northern latitudes. It is also a source of wild rubber (that is non-planted) in some central African countries.