There are eight species of eastern North American pitcher plants all occurring in the Atlantic coastal regions of North America. Of these, seven species are confined to the southeastern part of the United States where they typically inhabit wet, sandy areas in the pineland, sometimes localized and rather isolated, but often with two or more species sharing the same habitat. This often results in various hybridization. One species extends its distribution all the way northward deep into a large part of eastern Canada.

The genus name Sarracenia was adopted in honor of Dr. M. S. Sarrazin of Quebec, an early discoverer. The common name for the genus came from their hollow, tubular leaves which are shaped and function like pitchers.

Pitcher plants are herbaceous (non-woody) perennials consisting of a rhizome with thick fibrous roots. The hollow trap leaves arise directly from the rhizome above the ground. The pitcher leaves form a rosette and are erect or nearly so in most species but are decumbent in some. The lid develops at the upper end of the pitcher. The lid is typically reflected over the pitcher opening, but can develop to form a domed hood in some species. The mature pitchers range in height from 10 to 100cm, or even more at times, depending on the species and growing conditions.

A peculiar structure and a bizarre appearance of the pitcher leaves are, for centuries, the first to have attracted the attention of people. Linnaeus, who adopted the name Sarracenia, is one of the 18^th century botanists who believed -- erroneously, as many others did at the time -- that the lid of the pitcher is capable of movement in order to conserve the water within. Another botanist, Catesby, thought that the hollow leaves were a refuge for insects fleeing from animal predators. It was not until the beginning of the 19^th century that the more serious observations started to reveal the true carnivorous nature of the plants.

Trap Structure and Attraction

A close look at the pitcher plant shows that the hollow leaves are carefully constructed pitfalls designed to attract and capture small animal prey with amazing efficacy. Sometimes the colorful leaves are mistaken for flowers by visiting insects and uninitiated human observers alike. In fact, the pitcher leaves have evolved to exhibit all alluring elements of real flowers: Their visual lure of striking colors and patterns, copious nectar secretions, and a convenient landing site for flying insects. Some pitcher plants are known to release sweet attracting odor in addition to the nectar secretions. The ultra-violet photography of the pitcher also shows distinct UV absorption patterns for insect guidance as are commonly found in many insect-pollinating flowers.

Although the shape and the size of the pitchers are characteristic for each species, the basic structure and the function of the leaves are common to all species. The tubular pitcher leaf has a lid at the top, which is immobile. The brilliant colors and the nectar secretions along the lid margins and the lip of the pitcher mouth attract various kinds of small animal prey in the field including bees, flies, moths, mosquitoes, butterflies, spiders and ants. In fact, nectar is scattered over much of the outer surface of the pitcher as well where they form a nectar trail leading to the pitcher opening. The lid -- which often does not actually prevent rain water from entering the pitcher in some species due to varying degree of reflection over the pitcher opening -- may provide a convenient ramp and feeding ground for the insect visitors. Trying to lick nectar is a risky business, however, for venturing insects.

The inner surface of the pitcher is divided into several zones by various authors. The lid portion is the first zone (1) characterized by having many nectar glands. The inner surface of the lid is also covered by stiff, short hairs all pointing toward the pitcher opening. This is also where UV absorption pattern is most eminent. Just below near the pitcher mouth is the short region (2) where the hairs become shorter. This is where nectar secretionsis most abundant. Down below extends smooth, gland-free zone (3), half way into the pitcher. This is followed by the area (4) covered with long, thin, downward-pointing hairs intermeshing each other. This is a prey retention zone some calls an "eel-trap". Finally, at the bottom of the pitcher, (5) there is a short hair-free, gland-free region.

Some pitcher plant species -- the ones with the hooded lid -- develop areoles void of pigmentation around the hood. The fenestrations, as they are called, are white patches of small windows scattered toward the direction of the pitcher tube as seen from the pitcher rim. Insects have a tendency to fly their way out of the closed spaces in the direction of light. As the insect rests at the pitcher rim, these deceptive windows shine brightly. The flying insect bounces against the areoles as it attempts to fly through, gets exhausted, and  tumbles into the pitcher bottom. 

Digestion and Absorption

Pitcher plants possess digestive glands over the mid- to lower portions of the pitcher leaf interior (zones 1, 2 and 3). During the development of a pitcher leaf, the fluid is secreted in the pitcher interior while the pitcher is still closed. In this passive, pitfall type trap, the digestion of prey takes place in the solution retained at the pitcher bottom. The prey basically jumps into the pool of a pre-formulated bath of digestive fluid. Although, in many species, the rainwater dilutes the pitcher liquid, the acidity is known to be retained, at least in a younger leaf. Studies have shown that chemical stimulation by beef broth resulted in a multiple increase of fluid secretions of an unopened pitcher. The surface tension of the pitcher fluid is measured to be considerably lower than that of water. This promotes swift drowning of the insect prey by acting as a wetting agent to otherwise water-resistant surface of the insect body.

Researchers have been trying to determine the origin of enzyme during the digestive process. In spite of the studies confirming the protease secretions in the pitcher plants, at least in the younger leaves, it is generally believed that the digestion is heavily aided by bacterial actions externally introduced in the open pitcher during much of the pitcher leaf life cycle. The digestion process reduces the protein in the insect body into amino acid. The products of digestion are promptly absorbed by the digestive glands on the inner leaf surface.

Benefit

Pitcher plants typically grow in bogs, swamps, and wet sandy savannas where soils are often acid and deficient in major nutrients for the green plants, notably nitrates and phosphates. The question as to whether the carnivorous habit is essential to the survival of pitcher plants is not easily assessed. Experience shows the plants do well without trapping any animal prey in cultivation. Comparative experiments under a controlled situation also indicated, however, that in a long run, a group of plants well fed with animal prey grew more vigorously and produced more seeds. It is generally accepted that the habit of carnivory does benefit the pitcher plants typically growing in a poor soil. 

Inflorescence

The floral structure of pitcher plants is basically the same for all species. In the early spring, a tall scape emerging from the rosette center supports a solitary, nodding flower with showy coloration and rather odd appearance. The unique flower morphology of pitcher plants leads one to speculate an advanced floral adaptation, as in many an orchid flower, in terms of pollinator interactions. 

Nature often provides various mechanisms that prevent a plant from being fertilized by its own pollen. An obvious structural separation of pollen-receiving stigma outside the pollen chamber seems to encourage cross-pollination. When the pendulous flower opens facing down at the tip of the tall scape, a modified style assumes the shape of an inverted umbrella, with five points each having a tiny stigma notch projecting inward. The five petals hang along the umbrella between two points to form a corolla chamber, leaving the five stigma points outside. Numerous stamens surrounding the round ovary are confined inside the corolla chamber. This arrangement structurally separates pollen-producing anthers from stigmas located outside the corolla chamber. When an insect pollinator lands on the flower trying to find an entrance to the corolla chamber in search of nectar, a stigma at one of the umbrella points -- located at the parting of the petals -- is bound to be brushed and the pollen from the previously visited flowers are deposited. Once inside the corolla chamber, the insect seeks nectar at the base of the stamens. As it does so, the insect accumulates ample amount of pollen which probably has been accumulated on the umbrella floor inside the corolla. When the insect is ready to leave the flower, it is likely to push one of the hanging petals from the low point of the umbrella, rather than retrace the same petal parting. This way, the pollinator, now with the flower's own pollen, does not touch the stigma again, thus avoiding self-pollination.

??????? ======= Some field observation on one species showed, however, that the bees -- believed to be a dominant pollinator for pitcher plants among many insects visiting the flower -- often exited the flower the same way it had entered, presumably brushing the stigma again on exit, thereby increasing the danger of self-fertilization. In cultivation, it is well known among pitcher plants growers that artificial self-pollination almost invariably produces a good crop of viable seeds. It seems reasonable to conjecture that the floral structure of pitcher plants does encourage -- if not enforce -- cross-pollination, which is more advantageous form of sexual reproduction in creating more genetic variations within the species.

Seeds mature in July through September in the southeastern U.S. habitats, depending on the species and localities. In the warmer region, if the seeds are shed before the fall sets in, the germination takes place in a month or so, and tiny seedlings will emerge in that year, although the germination is often delayed until the following spring in many localities. In cultivation, it is a known practice to shed the seeds just before the full maturity and force the germination before or during the fall season. After twin cotyledons, a seedling produces tiny juvenile leaves which are already hollow, pitcher leaves. Shapes of the juvenile leaves are more or less the same for all species and do not exhibit distinct leaf characteristics of each species for a year or so. Pitcher plants usually mature from seedling to flowering age in 4 to 5 years. In nature as well as in cultivation, the bulb reproduction is common. The plants are said to live for 20-30 years.

Pollinator/Prey Dilemma

Pitcher plants being insect-pollinated, they must rely on the visiting insects to play the role of pollinating flowers on the one hand for the successful continuation of the species, and yet at the same time, must consume the insects as prey to supplement their nutritional need.

How do the pitcher plants reconcile this apparent paradox? There seem to be a few approaches taken by carnivorous plants in general. The "temporal" solution is one whereby flowers and traps are produced in different times of the season. This is the case for many pitcher plant species. Generally the inflorescence of the pitcher plants precedes the new pitcher leaf production by a month or so in the early spring. In the southeastern United States where many pitcher plants can be seen in savanna, mid-April through May is the height of flowering season for many species. It is observed that there aren't many new, active, pitchers produced at the time of flowering. 

Down south in Mobile, Alabama, S. alata blooms profusely in late April. There are no new leaves produced at that time. S. flava, which has a wide distribution from the Florida panhandle all the way to the north, produces golden yellow blossoms of large, dangling flowers in mass in North Caroline habitats in early May. The leaves from the previous year are all but completely blackened and decayed being pilled up at the base of the plants. There are practically no new leaves sprouting at the time of flowering for this species at this northern limit.

In addition to temporal separation, some carnivorous plants deploy "spatial" separation to resolve, at least in part, the dilemma of pollinator/prey differentiation. In S. psittacina and S. purpurea species, a tall scape (relative to their leaf height) positions the flower well above the trapping space occupied by the pitcher openings. Many erect species also produce their flowers on the scape taller than their pitchers.

Mutualism

The observations in the field, as well as in cultivation, show that many of potential prey attracted by the nectar secretionsof the pitcher -- and presumably having enjoyed the nectar -- do leave the plants without being caught. 

This leads to a consideration by some researcher that the pitcher plants provide nectar for certain insect communities in a mutually beneficial way, thus forming "mutualism": Insect communities benefit by receiving nectar from pitcher plants -- in exchange for a small portion of the community being sacrificed as prey.

(On the other hand, considering the number of flying and crawling insects visiting the pitcher during the active season, if all or almost all visitors were successfully caught in the process, any pitcher leaf would be filled to the gills in a matter of days or even hours.)