What species is the jalapeño pepper used in many guacamole recipes?

The jalapeño pepper used in many guacamole recipes belongs to the species Capsicum annuum.

Jalapeño is a cultivar, or cultivated variety, of this species rather than a separate species of its own. Capsicum annuum also includes bell peppers, poblanos, cayenne peppers, and several other familiar chiles, so the species contains peppers with widely different shapes and heat levels.

Jalapeños are commonly harvested while green, when they typically measure about 4,000–8,500 Scoville heat units. If left on the plant, they ripen to red, orange, or yellow and may become somewhat sweeter. The smoky dried form is called a chipotle.

A common mix-up is confusing the species name with the genus: Capsicum is the genus, while annuum identifies the species. Habaneros belong to a different species, Capsicum chinense, and tabasco peppers are usually classified as Capsicum frutescens.