From Wikipedia: “The chili pepper… is the fruit of plants from the genus Capsicum, members of the nightshade family, Solanaceae. They are widely used in many cuisines to add spiciness to dishes. The substances that give chili peppers their intensity when ingested or applied topically are capsaicin and related compounds known as capsaicinoids.
Chili peppers originated in Mexico. After the Columbian Exchange, many cultivars of chili pepper spread across the world, used for both food and traditional medicine. Worldwide in 2014, 32.3 million tonnes of green chili peppers and 3.8 million tonnes of dried chili peppers were produced. China is the world's largest producer of green chillies, providing half of the global total.”
Species and cultivars:
“Though there are only a few commonly used species, there are many cultivars and methods of preparing chili peppers that have different names for culinary use. Green and red bell peppers, for example, are the same cultivar of C. annuum, immature peppers being green. In the same species are the jalapeño, the poblano (which when dried is referred to as ancho), New Mexico, serrano, and other cultivars.
Peppers are commonly broken down into three groupings: bell peppers, sweet peppers, and hot peppers. Most popular pepper varieties are seen as falling into one of these categories or as a cross between them.”
“While red chilies contain large amounts of vitamin C, other species contain significant amounts of provitamin A beta-carotene. In addition, peppers are a rich source of vitamin B6.”
“Chili pepper pods, which are berries, are used fresh or dried. Chilies are dried to preserve them for long periods of time, which may also be done by pickling.
Dried chilies are often ground into powders, although many Mexican dishes including variations on chiles rellenos use the entire chili. Dried whole chilies may be reconstituted before grinding to a paste. The chipotle is the smoked, dried, ripe jalapeño.
Many fresh chilies such as poblano have a tough outer skin that does not break down on cooking. Chilies are sometimes used whole or in large slices, by roasting, or other means of blistering or charring the skin, so as not to entirely cook the flesh beneath. When cooled, the skins will usually slip off easily… Fresh or dried chilies are often used to make hot sauce, a liquid condiment—usually bottled when commercially available—that adds spice to other dishes. Hot sauces are found in many cuisines including harissa from North Africa, chili oil from China (known as rāyu in Japan), and sriracha from Thailand.”
“The substances that give chili peppers their pungency (spicy heat) when ingested or applied topically are capsaicin (8-methyl-N-vanillyl-6-nonenamide) and several related chemicals, collectively called capsaicinoids. The quantity of capsaicin varies by variety, and on growing conditions. Water stressed peppers usually produce stronger pods. When a habanero plant is stressed, for example low water, the concentration of capsaicin increases in some parts of the fruit.
When peppers are consumed, capsaicin binds with pain receptors in the mouth and throat, potentially evoking pain via spinal relays to the brainstem and thalamus where heat and discomfort are perceived. The intensity of the "heat" of chili peppers is commonly reported in Scoville heat units (SHU). Historically, it was a measure of the dilution of an amount of chili extract added to sugar syrup before its heat becomes undetectable to a panel of tasters; the more it has to be diluted to be undetectable, the more powerful the variety, and therefore the higher the rating. The modern method is a quantitative analysis of SHU using high-performance liquid chromatography (HPLC) to directly measure the capsaicinoid content of a chili pepper variety. Pure capsaicin is a hydrophobic, colorless, odorless, and crystalline-to-waxy solid at room temperature, and measures 16,000,000 SHU.”
Medicinal and other uses:
“Capsaicin, the chemical in chili peppers that makes them hot, is used as an analgesic in topical ointments, nasal sprays, and dermal patches to relieve pain.
Capsaicin extracted from chilies is used in pepper spray as an irritant, a form of less-lethal weapon.”
“The name of the plant is almost certainly unrelated to that of Chile, the country, which has an uncertain etymology perhaps relating to local place names.”