Piper, the pepper plants or pepper vines (a term used for certain Clematis in older times), are an economically and ecologically important genus in the family Piperaceae. It contains about 1,000-2,000 species of shrubs, herbs, and lianas, many of which are keystone species in their native habitat The diversification of this taxon is of interest to understanding the evolution of plants.
Pepper plants belong to the magnoliids, which are very ancient angiosperms. Their family, Piperaceae, is most closely related to the lizardtail family (Saururaceae), which in fact generally look like smaller, more delicate and amphibious pepper plants. Both families have characteristic tail-shaped inflorescences covered in tiny flowers. A somewhat less close relative is the pipevine family (Aristolochiaceae). A well-known and very close relative – being also part of the Piperaceae – are the radiator plants of the genus Peperomia.
Most Piper species are either herbaceous or vines; some grow as shrubs or almost as small trees. A few species, commonly called "ant pipers" (e.g. Piper cenocladum), live in a mutualism with ants. In the wild, peppercorns get distributed mainly by birds, but small fruit-eating mammals – e.g. bats of the genus Carollia – are also important. Despite the high content of chemicals that are noxious to herbivores, some have evolved the ability to withstand the chemical defences of pepper plants, for example the sematurine moth Homidiana subpicta or some flea beetles of the genus Lanka. The latter can be significant pests to pepper growers.
Unsustainable logging of tropical primary forests is threatening a number of peppers. The extent of the effect of such wholesale habitat destruction on the genus is unknown, but it is to be noted that in the forests of Ecuador – the only larger region for which comprehensive data exists – more than a dozen species are known to be on the brink of extinction. On the other hand, other Piper species (e.g. Spiked Pepper, P. aduncum) have been widely distributed as a result of human activity and are a major invasive species in certain areas.
The most significant human use of Piper is not for its looks however, but ultimately for the wide range of powerful secondary compounds found particularly in the fruits.
Use of peppercorns as pungent spice is significant on an international scale. In the Antiquity, there was a vigorous trade of spices including Black Pepper (P. nigrum) from South Asia to Europe already. The Apicius, a recipe collection complied about 400 AD, mentions "pepper" as a spice for most main dishes, though in some cases the unrelated Allspice (Pimentum dioica) rather than of Black Pepper might have been used. Judging from the Apicius, in the late Roman Empire, Black Pepper was probably still expensive, but nevertheless seems to have been available readily enough to be used more frequently than salt or sugar. As Europe turned into the Early Middle Ages, trade routes deteriorated and the use of pepper declined somewhat.
But this dearth was hardly ever absolute and altogether rather short-lived. Black peppercorns, storing easily and having a high mass per volume, never ceased to be a profitable trade item. In the Middle Ages, international traders were nicknamed Pfeffersäcke ("pepper-sacks") in German towns of the Hanseatic League and elsewhere. As the Modern Era came into full swing, wars were fought by European powers, between themselves and in complex alliances and enmities with Indian Ocean states, about control of the supply of spices, perhaps the most archetypal being Black Pepper fruit. Today, Black Pepper corns of the three preparations (green, white and black) are one of the most widely used spices of plant origin worldwide.
Due to the wide distribution of Piper, the fruit of other species are also important spices, many of them internationally. Mecaxochitl (P. amalgo) was used by the Aztecs to spice up cocoa. Cubeb (P. cubeba), also known as Tailed or Javan Pepper actually played a major role in Early Modern Era spice trade; ocet kubebowy, Cubeb-flavored vinegar, was a popular condiment in 14th century Poland. But reputedly Philip IV of Spain at the end of the 1630s suppressed trade in Cubeb peppercorns to capitalize on his massive share of the Black Pepper trade. After a brief comeback as a medical plant, Cubeb is nowadays fairly obscure in the West. It is however a most significant spice around the Indian Ocean region today, and popular as far as Morocco where it flavors spicy-sweet markout pastry and is sometimes included in the famous ras el hanout mix. Further east, it is well-loved across Indonesia, where it is the popular pepper to use in gulé (curried stews).
West African Pepper (P. guineense), also given a variety of "regionalized" names like "Benin pepper", "Ashanti pepper, or the rather ambiguous "Guinea pepper", is considered supreme for use in stews and other regional specialties. It is used in addition to Black Pepper to impart a particularly refined aroma with hints of nutmeg and saffron. Sometimes it is used in the East African berbere spice mix. This species, despite being traded more extensively in earlier times, is very hard to get outside Africa today. More readily available in the West is Long Pepper (P. longum), commonly traded under its Indian name pipalli. This is possibly the secondmost popular Piper spice internationally; it has a rather chili-like "heat" and the whole inflorescence is used as the fruits are tiny.
Not only the seeds of Piper are used in cooking. West African Pepper leaves, known locally as uziza, are used as flavoring vegetable in Nigerian stews. In Mexican-influenced cooking, hoja santa or Mexican Pepperleaf (P. auritum) has a variety of uses, mainly to impart flavor too. In Southeast Asia, leaves of two species of Piper have major importance in cooking: Lolot (P. lolot) is used to wrap meat for grilling in the Indochina region, while P. sarmentosum, often seen under the name cha phlu, is used raw or cooked as a vegetable in its own right in Malay and Thai cuisine; it is also used to prepare the famous miang snacks of Tak Province.
Cubeb (P. cubeba) has been used in folk medicine, herbalism and related fields (e.g. alchemy, folk magic or exorcism), as well as, particularly in the early 20th century, as a cigarette flavoring. P. darienense is used medically by the Kuna people of the Panama-Colombia border region, and elsewhere it is used to intoxicate fish which then can be easily caught. Spiked Pepper, often called "matico", appears to have strong disinfectant and antibiotic properties. Black Pepper (P. nigrum) essential oil is sometimes used in herbalism, and Long Pepper (P. longum) is similarly employed in Ayurveda, where it was an ingredient of Triphala Guggulu and (together with Black Pepper) of Trikatu pills, used for rasayana (rejuvenating and detoxifying) purposes.Piper species have gained large-scale use as a stimulant. Betel (P. betle) is used as a wrapper for the Betel leaf chunks; its sap helps release the stimulating effect of these "cookies" which are widely known as pan in India. In the Pacific region, where it has been widely spread as a canoe plant, Kava (P. methysticum) is used to produce a stimulating drink somewhat similar to alcohol but without many of the negative side effects and addiction risk. It has also become popular elsewhere in recent decades, and is used as a medical plant. However, Kava whole-plant "herbal supplement" pills have occasionally shown a strong hepatotoxic effect, which has led to their banning in many countries. On the other hand, the traditional preparation of the root as a stimulating drink appears to pose little if any such hazard.
Piper is a model genus for research in ecology and evolutionary biology. The diversity and ecological importance of the genus makes it an obvious candidate for ecological and evolutionary studies, though not surprisingly, most research has focused on the economically important species P. nigrum (black pepper), P. methysticum (kava), and P. betle (betel).
The obligate and facultative ant mutualists found in some Piper species have a strong influence on their biology, making them ideal systems for research on the evolution of symbioses and the effect of mutualisms on biotic communities.
Important secondary metabolites found in pepper plants are piperine and chavicine, which were first isoalted from Black Pepper. The piperidine functional group is named after the former, and piperazine (which is not found in P. nigrum in noticeable quantities) was in turn named after piperidine.