The trees and plants whose latices furnish caoutchouc in considerable quantity chiefly belong to the natural orders Euphorbiaceae, Urticaceae, Apocynaceae, Asclepiadaceae.
African (Ire or Irai or Lagos) rubber tree, which belongs to the Apocynaceae, a natural order which includes the Landolphia vines as well as other rubber producers.
Of the Apocynaceae the rubber plants are the most important.
This arrangement is characteristic of the flower-buds of Malvaceae and Apocynaceae, and it is also seen in Convolvulaceae and Caryophyllaceae.
When the flower expands, the traces of twisting often disappear, but sometimes, as in Apocynaceae, they remain.
The union is usually most complete at the base; but in Labiatae the styles are united throughout their length, and in Apocynaceae and Asclepiadaceae the stigmas only.