Jalapenos are generally dark green, although some varieties may turn red when they mature. The peppers are approximately 2 to 3 inches in length, and they are wider at the stem end and have a blunt tip. The name of the pepper is derived from Jalapa, a city in the Mexican state of Veracruz that was once a major production center for the jalapeno.
Standard varieties of jalapeno include Jalapeno Early, a hot pepper 2 to 3 inches long with a thick flesh that turns red as it matures, and Jalapeno M, sometimes referred to as Jalapeno Jumbo or Jalapeno Santiago. This pepper is the most common variety grown in Mexico. It grows up to 3 inches in length, is dark green, and matures to a scarlet red color. Standard varieties of jalapeno peppers are still grown in three main areas of Mexico: south of Veracruz and north of Oaxaca along the lower basin of the Papaloapan River; north of Veracruz; and in the region of Delicias, Chihuahua. Many of these varieties are also grown in the United States.
Many varieties of hybrid jalapenos, known as designer peppers, have been developed in recent years. These chiles are bred for a specific purpose or to open new markets for farmers. Hybrid peppers may be bred for ornamentation, such as Numex Pinata, a chile that goes from light green to yellow to orange to red. Or they may be bred for flavor, such as the Numex Primavera, which is a very mild jalapeno. Numex Jamlamundo is a jalapeno bred for size, and it is well-suited to be stuffed for culinary dishes, such as jalapeno poppers. Many hybrids are bred for easy growing. Jalapeno Agriset, for instance, developed from Agriset seeds, fruits earlier than many varieties, does not crack and provides higher yields.
Scoville units measure the "heat" of a chile pepper, which is determined by the concentration of capsaicin, the active component in chile peppers that makes them spicy. Most traditional varieties of jalapenos have medium heat, measuring between 3,500 to 4,500 Scoville units. The hottest varieties, such as Grande, only reach 4,502 Scoville units, which is mild compared to other types of chile peppers, such as the habanero, which has as much as 200,000 to 300,000 Scoville units. Some of the newer hybrid jalapeno peppers are hotter than the traditional varieties. The Scoville units in Jalapeno Telica, for instance, are rated between 6,000 and 8,000. On the other hand, Jalapeno TAM Veracruz F1, developed by Texas A&M Univeristy, was bred to be mild; its heat is rated between 1,000 and 3,500 Scoville units.