What is the hottest pepper used in Mexican cuisine?

It's difficult to definitively say which is the "hottest" pepper used in Mexican cuisine, as there are many varieties, and "hotness" is subjective. However, some of the most popular and very spicy peppers commonly used in Mexican cooking include:

* Habanero: This fiery pepper is known for its intense, fruity heat and is often used in salsas, sauces, and dishes like "chile rellenos" (stuffed peppers).

* Serrano: These peppers are versatile and offer a good balance of heat and flavor, making them popular in salsas, guacamole, and as a garnish.

* Jalapeño: While not as hot as habaneros, jalapeños still deliver a good kick and are a staple in Mexican cooking, used in everything from salsas to tacos to chili con carne.

* Chipotle: These are smoked jalapeños, offering a unique flavor profile with both smokiness and heat. They are often used in salsas, adobo sauces, and other dishes.

* Guajillo: These peppers are dried and offer a medium-hot heat with earthy and slightly sweet notes. They are commonly used in moles, salsas, and stews.

Ultimately, the "hottest" pepper depends on your individual heat tolerance and the dish you're preparing.

It's important to note that some regions in Mexico specialize in specific pepper varieties, and the usage of different peppers might vary depending on the local cuisine and traditions.