The Thai ingredient from the Americas that is paired with rice in importance is the chili pepper.
Rice is the foundation of Thai meals, and chili peppers became the cuisine’s defining source of heat. Thai cuisine describes chili peppers and rice as two of its most important ingredients, even though chilies are a relatively late arrival. Before their introduction, cooks used spices such as black pepper, long pepper and Sichuan pepper to create pungency.
Chili peppers originated in the Americas, where people cultivated them for thousands of years. Portuguese traders and emissaries probably carried them to Asia during the 16th century as part of the Columbian Exchange. Thai cooks eventually incorporated them into curry pastes, nam phrik, soups, stir-fries and salads.
The ingredient is not the same as pineapple, papaya or tomato, all of which also reached Southeast Asia from the Americas. Those foods became important in particular dishes, but chili peppers gained a much broader role in Thai flavor-building and culinary identity.