Cacao trees (Theobroma cacao L.) are divided into three morphological types: Criollo, Forastero, and Trinitario.
Criollo trees produce the most valuable beans, with better flavor and less bitterness than other types. Unfortunately, they are are vulnerable to disease and have lower bean yields. The lower yields mean that even with substantially higher Criollo bean prices, they generate less revenue for farmers than planting with Forastero or Trinitario. Criollo trees are grown primarily in Venezuela, Columbia, Comoros, Grenada, Jamaica, Java, Madagascar and Trinidad. Between 1% and 5% of the annual world production is Criollo.
Forastero trees are often subdivided into lower Amazon Forastero and upper Amazon Forastero in terms of genetics, but since the chocolate created from both Forastero varieties is generally considered inferior, they are simply called Forastero from a consumer perspective. Both types of Forastero produce higher bean yields and are much more resistant to disease than Criollo, and as a result, are used in most cacao plantations. They are grown in the Ivory Coast, Brazil, Cameroon, Columbia, Ecuador, French Guyana, Ghana, Guyana, Indonesia, Nigeria, Peru, São Tomé, Venezuela, and other countries of West Africa, South America, and Southeast Asia. Between 80% and 90% of the world production is Forastero.
Trinitario trees are a hybrid of Criollo and Forastero trees, originally from Trinidad, and are now grown in many countries, including Cameroon, Ecuador, Java, Lesser Antilles, Papua New Guinea, Samoa, Sri Lanka, and Venezuela. Acquiring much of the quality of Criollo and the increased yield and disease-resistance of Forastero, Trinitario has become a popular cacao tree among plantations selling to artisan chocolate makers. Between 10% and 20% of the world production is Trinitario.
A recent study published in 2008 suggests that the traditional division into three types of cacao trees does not accurately reflect their genetic diversity. Instead, they propose a new classification of 10 types: Amelonado, Contamana, Criollo, Curaray, Guiana, Iquitos, Marañon, Nanay, Nacional and Purús. Until such a change is widely accepted, I'll continue to use the traditional classification into Criollo, Forastero, or Trinitario.
Note: the ranges of values for world production are because I did not find reliable data, and instead combined data from multiple unconfirmed sources.