There are several distinct species of the vanilla orchid used for food flavouring, the most common being vanilla planifolia, vanilla tahitiensis and vanilla pompona (in that order).
Vanilla planifolia is usually marketed as "Bourbon vanilla", most of which is grown in Indonesia and Madagascar. The same species is also grown in Mexico, but they have decided to call it "Mexican vanilla", which is purely a marketing designation. At least the Mexicans claim their vanilla to be of superior quality, but the vanilla extracts sold in Mexico are often stretched with tonka bean extract, which has a similar taste and aroma to vanilla, but contains coumarin, which is banned as a food additive by the US Food & Drug Administration. Other countries have less strict regulations, often only regulating a maximum coumarin content.