The family Sarraceniaceae consists of three genera of pitcher plants and is distributed throughout North America and the western portion of the Guiana Highlands in South America. Members of this family commonly inhabit bogs, swamps, wet or sandy meadows, and savannas where the soils are water-saturated, acidic, and deficient in nutrients. The carnivorous traps of this family commonly resemble trumpets, pitchers, or urns and primarily capture insects.
The genusSarracenia, sometimes known as the trumpet pitcher genus, consists of some 10 species native to eastern North America. Insects are attracted to the mouth of the pitcher by a trail of nectar-secreting glands that extend downward along the lip to the interior of the pitcher. The throat of the pitcher, just below the lip, is very smooth and sends the insect tumbling down into the liquid pool at the bottom of the pitcher, where it drowns. The insect is then digested by enzymes secreted within the leaf. The purple, or common, pitcher plant (S. purpurea) has heavily veined, green to reddish, flaring, juglike leaves that bear downward-pointing bristles to keep prey from escaping. Its flowers are purple-red. The parrot pitcher plant (S. psittacina) has small, fat, red-veined leaves that are topped by beaklike lids and bears dark red flowers. The sweet pitcher plant (S. rubra) produces dull red, violet-scented flowers. The crimson pitcher plant (S. leucophylla) has white trumpet-shaped pitchers with ruffled upright hoods and scarlet flowers. The yellow pitcher plant (S. flava) has bright yellow flowers and a long, green, trumpet-shaped leaf the lid of which is held upright.
The cobra plant (Darlingtonia californica) is the only species of its genus and is native to swamps in mountain areas of northern California and southern Oregon. Its hooded pitcherlike leaves resemble striking cobras and bear purple-red appendages that look similar to a snake’s forked tongue or a set of fangs. Unlike other pitcher plants, the cobra plant does not appear to produce digestive enzymes and instead relies on bacteria to break down its prey.
The genus Heliamphora, known as sun pitchers or marsh pitcher plants, consists of some 23 species native to the rainforest mountains of western Brazil, Guyana, and Venezuela. These species form cushions on ridge crests and swampy depressions and bear stout pitchers that can attain a height of 50 cm (20 inches).
The family Nepenthaceae consists of a single genus, Nepenthes, with some 140 species of tropical pitcher plants native to Madagascar, Southeast Asia, and Australia. Most of these species are perennials that grow in very acidic soil, though some are epiphytic and live on the branches of trees. The lid of the pitcher secretes nectar to attract prey, which are unable to escape from the trap because of its downward-pointing hairs and slick sides. This genus includes the endangeredAttenborough’s pitcher plant (N. attenboroughii), which is one of the largest of all carnivorous plants, reaching up to 1.5 metres (4.9 feet) tall with pitchers that are 30 cm (11.8 inches) in diameter. Found near the summit of Mount Victoria on the island of Palawan in the Philippines, Attenborough’s pitcher plant is capable of capturing and digesting rodents, as well as insects and other small animals. Cultivated species of pitcher plants from the Old World genus Nepenthes include the slender pitcher plant (N. gracilis), the common swamp pitcher plant (N. mirabilis), and the golden peristome (N. veitchii), as well as a number of hybrid species such as Hooker’s pitcher plant N. ×hookeriana, N. ×mastersiana, and N. ×dominii.
Pitcher plants are several different carnivorous plants which have modified leaves known as pitfall traps—a prey-trapping mechanism featuring a deep cavity filled with digestive liquid. The traps of what are considered to be "true" pitcher plants are created from modified leaves; however they are not simply folded into a tube, and the process is far more complex. They attract insects by using sweet, delicious nectar causing them to drown in it.
The term "pitcher plant" generally refers to members of the Nepenthaceae and Sarraceniaceae families, but similar pitfall traps are employed by the monotypic Cephalotaceae and some members of the Bromeliaceae. The families Nepenthaceae and Sarraceniaceae are the most species-rich families of pitcher plants.
The Nepenthaceae contains a single genus, Nepenthes, containing over 100 species and numerous hybrids and cultivars. In these Old World pitcher plants, the pitchers are borne at the end of tendrils that extend from the midrib of an otherwise unexceptional leaf. 'Old world' pitcher plants (genus: Nepenthes) are typically characterized as having reduced and symmetrical pitchers with a comprehensive waxy coating on the surface of the inner pitcher wall. The plants themselves are often climbers, accessing plants (Sarraceniaceae), which comprise three genera, are ground-dwelling herbs whose pitchers arise from a horizontal rhizome. In this family, the entire leaf forms the pitcher, as opposed to Nepenthaceae where the pitcher arises from the terminal portion of the leaf. The species of the genus Heliamphora, which are popularly known as marsh pitchers (or erroneously as sun pitchers), have a simple rolled-leaf pitcher, at the tip of which is a spoon-like structure that secretes nectar. They are restricted to areas of high rainfall in South America. The North American genus Sarracenia are the trumpet pitchers, which have a more complex trap than Heliamphora, with an operculum, which prevents excess accumulation of rainwater in most of the species. The single species in the Californian genus Darlingtonia is popularly known as the cobra plant, due to its possession of an inflated "lid" with elegant false-exits, and a forked "tongue", which serves to ferry ants and other prey to the entrance of the pitcher. The species in the genus Sarracenia readily hybridise, making their classification a complex matter.
The Cephalotaceae is a monotypic family with but one genus and species, Cephalotus follicularis. This species has a small (2–5 cm) pitcher similar in form to those of Nepenthes. It occurs in only one location in southwestern Australia.
A few species of bromeliads (Bromeliaceae), such as Brocchinia reducta and Catopsis berteroniana, are known or suspected to be carnivorous. Bromeliads are monocots, and given that they all naturally collect water where their leaves meet each other, and that many collect detritus, it is not surprising that a few should have been naturally selected to develop the habit into carnivory by the addition of wax and downward-pointing hairs.
The purple pitcher plant, Sarracenia purpurea, is the floral emblem of the province of Newfoundland and Labrador, Canada.
Foraging, flying or crawling insects such as flies are attracted to the cavity formed by the cupped leaf, often by visual lures such as anthocyanin pigments, and nectar bribes. The rim of the pitcher (peristome) is slippery, when moistened by condensation or nectar, causing insects to fall into the trap. Pitcher plants may also contain waxy scales, protruding aldehyde crystals, cuticular folds, inward and downward pointing (retrorse) hairs, or guard-cell-originating lunate cells on the inside of the pitcher to ensure that insects cannot climb out. The small bodies of liquid contained within the pitcher traps are called phytotelmata. They drown the insect, and the body of it is gradually dissolved. This may occur by bacterial action (the bacteria being washed into the pitcher by rainfall) or by enzymes secreted by the plant itself. Furthermore, some pitcher plants contain mutualistic insect larvae, which feed on trapped prey, and whose excreta the plant absorbs. Whatever the mechanism of digestion, the prey items are converted into a solution of amino acids, peptides, phosphates, ammonium and urea, from which the plant obtains its mineral nutrition (particularly nitrogen and phosphorus). Like all carnivorous plants, they all grow in locations where the soil is too poor in minerals and/or too acidic for most plants to survive. Rather than relying on photosynthetic glucose to survive, pitcher plants supplement available nutrients and minerals (which plants normally obtain through their roots) with the constituents of their insect prey.
Mature plants of Nepenthes lowii attract tree shrews (Tupaia montana), which feed on nectar that the plant produces but also defecate into the pitcher, providing nitrates and other nutrients. The plant and tree shrew have a symbiotic relationship. The rim of N. lowii is not slippery so that tree shrews can easily get in and out, and it provides more nectar than other pitcher plants. The shape of the pitcher rim and the position of the nectar ensure that the animal's hindquarters are over the rim while it feeds.
Evolution of the form
It is widely assumed pitfall traps evolved by epiascidiation (infolding of the leaf with the adaxial or upper surface becoming the inside of the pitcher), with selection pressure favouring more deeply cupped leaves over evolutionary time. The pitcher trap evolved independently in three eudicot lineages and one monocot lineage, representing a case of convergent evolution. Some pitcher plant families (such as Nepenthaceae) are placed within clades consisting mostly of flypaper traps, indicating that some pitchers may have evolved from the common ancestors of today's flypaper traps by loss of mucilage.
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