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Encyclopedia: carnivore, Carnivorous plant, The Carnivorous Carnival, Carnivorous Leech, Carnivorous_plant, Ashot I, Category:Carnivorous plants, Talk:Carnivorous plant, Image:Carnivorous carnival uk.jpg, Talk:The Carnivorous Carnival

carnivorous plant (sometimes called an insectivorous plant) is a plant that derives some or most of its
nutrients (but not energy) from trapping and consuming animals or protozoans,
especially insects and other arthropods. Carnivorous plants usually
grow in places where the soil is thin or poor in nutrients,
especially nitrogen, such as acidic bogs (moss in Scotland) and rock outcroppings.
Charles Darwin wrote the first well-known treatise on carnivorous plants in 1875.cite book | author=Darwin C | title=Insectivorous plants | publisher=John Murray | location=London | year=1875 |

Trapping mechanisms

There are five basic trapping mechanisms that are found in carnivorous plants. These are:

#Pitfall traps (pitcher plants), which trap prey in a rolled leaf that contains a pool of digestive enzymes and/or bacteria;
#Flypaper traps, which trap prey using a sticky mucilage;
#Snap traps, which trap prey with rapid leaf movements;
#Bladder traps, which suck in prey with a bladder that generates an internal vacuum;
#Lobster-pot traps, which use inward pointing hairs to force prey to move towards a digestive organ.

These traps may also be classified as active or passive, depending on whether movement aid the capture of prey. For example, there are both passive flypapers,
such as Triphyophyllum, which secrete mucilage, but whose leaves do not
grow or move in response to prey capture; and there are also active flypapers, such as
sundews, whose leaves undergo rapid growth, aiding in the retention and
digestion of prey.

Pitfall traps

Pitfall traps are thought to have evolved independently on at least four occasions. The simplest pitfall
traps are probably those of Heliamphora, the sun pitcher plant.
In this genus, the traps are quite clearly evolutionarily derived from a simple
rolled leaf whose margins have sealed together. These plants live in areas of
high rainfall in South America (such as Mount Roraima), and consequently have a problem ensuring their
pitchers do not overflow. To counteract this problem, natural selection has favoured the
evolution of an overflow, similar to that of a bathroom sink: there is a small gap in the
zipped up leaf-margins that allows excess water to flow out of the pitcher.

thumb|200px|left|operculum (nectar spoon) ">[Heliamphora: note the very small operculum (nectar spoon) ]

Heliamphora is a member of the Sarraceniaceae, a New World family in the
order Ericales (heathers and allies). Heliamphora is limited to South America,
but the family contains two other genera, Sarracenia and Darlingtonia,
which are endemic to Florida (for the most part) and California respectively. S. purpurea subsp. purpurea (the northern pitcher plant) has a more cosmopolitan distribution, being found as far north as Canada.
Sarracenia is the pitcher plant genus most commonly encountered in cultivation, because it is relatively hardy and easy to grow.

thumb|220px|right|Darlingtonia: note the small entrance to the trap underneath the swollen 'balloon', and the colourless patches that confuse prey trapped inside.]

In the genus Sarracenia, the problem of pitcher overflow is solved by an
operculum, which is essentially a flared leaflet that covers the opening of the
rolled-leaf tube, and protects it from rain. Possibly because of this improved
waterproofing, species of Sarracenia secrete enzymes such as proteases and phosphatases into the digestive
fluid at the bottom of the pitcher; Heliamphora relies on bacterial digestion alone. These enzymes digest the proteins and nucleic acids in the prey, releasing amino acids and phosphate ions, which the plant absorbs.
Darlingtonia californica, the cobra plant, possesses an adaptation also found in
Sarracenia psittacina and to a lesser extent in Sarracenia minor:
the operculum is balloon-like, and almost seals the opening to the tube. This balloon-like chamber is
pitted with areolae, which are chlorophyll-free patches through which light can penetrate.
Insects (mostly ants) enter the chamber via the opening, which is underneath
the balloon, and once inside, tire themselves trying to escape from these false
exits, until they eventually fall into the tube. Prey access is increased by the 'fish tails' (outgrowths of the operculum), which give the plant its name. Some seedling Sarracenia species also have long, overhanging opercular outgrowths: Darlingtonia may therefore represent an example of neoteny.

The second major group of pitcher plants are the monkey cups or tropical
pitcher plants of the genus Nepenthes. In the hundred or so species of this genus,
the pitcher is born at the end of a tendril, which grows as an extension to the midrib
of the leaf. Most species catch insects, although the larger ones, particularly
N. rajah, will also occasionally take small mammals and reptiles. These pitchers represent
a convenient source of food to small insectivores: N. bicalcarata possesses two sharp thorns
that project from the base of the operculum over the entrance to the pitcher, which provide
some protection from raids by freeloading mammals.

thumb|200px|left|[Brocchinia: a carnivorous bromeliad]

The pitfall trap has evolved independently in at least two other groups. Cephalotus follicularis,
the Albany pitcher plant, is a small pitcher plant from Western Australia, with
moccasin-like pitchers. In this species, the rim of the pitcher's opening (the peristome)
is particularly pronounced, and both secretes nectar, and provides a thorny overhang to the
opening, which prevents trapped insects from climbing out. The lining of most pitcher plants
is covered in a loose coating of waxy flakes, which provides a very uncertain footing for insects. The insects are often attracted by nectar bribes secreted by the peristome, and by bright flower-like anthocyanin patterning.
In at least one species (Sarracenia flava), the nectar bribe is laced with coniine, a
toxic alkaloid also found in hemlock, which probably increases the efficiency of the traps by intoxicating the prey items.

The final carnivore with a pitfall-like trap is the bromeliad, Brocchinia reducta.
Like most relatives of the pineapple, this species has an urn, formed from the tightly-packed,
waxy leaf bases of the strap-like leaves. In most bromeliads, water collects readily in this urn, and
may provide habitats for frogs, insects and (more usefully for plant)
diazotrophic (nitrogen-fixing) bacteria. In Brocchinia, the urn is specialised as an
insect-trap, with a population of digestive bacteria, and a loose, waxy lining.

Flypaper traps

thumb|250px|right|[Pinguicula: the leaves and even the flower stems are covered in mucilage-secreting glands which trap insects.]
The flypaper traps are those whose trapping mechanism is based on a sticky mucilage, or glue. The leaf of flypaper traps is studded with
mucilage-secreting glands, which may either be short and nondescript (like those of
the butterworts), or long and mobile (like those of many sundews). Flypapers have evolved independently at least five times.

In the genus Pinguicula, the mucilage glands are quite short (sessile), and the
leaf, whilst shiny (giving the genus its common name of 'butterwort'), does not superficially
appear carnivorous. However, this belies the fact that the leaf is an extremely
effective trap of small flying insects (such as fungus gnats), and whose surface responds
to prey by relatively rapid growth. This thigmotropic growth may involve rolling of the leaf blade (to prevent
rain from splashing the prey off the leaf surface), or 'dishing' of the surface
under the prey, to form a shallow digestive pit.

thumb|150px|left|A sundew with a captured flyThe sundew genus (Drosera) consists of over 100 species of active flypapers, whose
mucilage glands are borne at the end of long tentacles, which frequently grow fast enough
in response to prey (thigmotropism) to aid the trapping process. The tentacles of D. burmanii are capable of
bending 180° in only a minute or so. Sundews are extremely cosmopolitan, and are found
on all the continents except the Antarctic mainland. They are probably at their
most diverse in Australia, the home of the large subgroup of pygmy sundews, such as D. pygmaea, and a number of tuberous sundews such as D. peltata, which form tubers that aestivate during the dry summer months.
These species are so dependent on insect sources of nitrogen that they generally lack the
enzyme (nitrate reductase), which most plants require to assimilate soil-borne nitrate into organic forms.

Closely related to Drosera is the Portuguese dewy pine, Drosophyllum, which differs from
the sundews in being passive: the leaves are incapable of rapid movement or growth. Unrelated, but
similar in habit, are the Australian rainbow plants (Byblis). Drosophyllum
is unusual amongst carnivores in that it grows under near-desert conditions: almost all other
carnivores are either bog plants or grow in moist tropical areas.

Recent molecular data (particularly the production of plumbagin) indicate that the remaining flypaper, Triphyophyllum peltatum, a member of the Dioncophyllaceae is closely related to Drosophyllum, and forms part of a larger clade of carnivorous and non-carnivorous plants with the Droseraceae, Nepenthaceae, Ancistrocladaceae and Plumbaginaceae. This plant is usually
encountered as a liana, however, in its juvenile phase, the plant is carnivorous: this
may be related to a requirement for specific nutrients for flowering.

Snap traps

thumb|right|200px|Snap traps close rapidly when triggered to trap prey between two lobes
There are only two active snap-traps, which are believed to have had a common ancestor with similar adaptations. These
are the Venus flytrap (Dionaea muscipula) and the waterwheel plant (Aldrovanda vesiculosa). The trapping mechanism of these plants has also been described as a 'mouse trap' or 'man trap', based on their shape and/or rapid movement; however, snap trap is generally preferred as these other designations are misleading, particularly with respect to the intended prey. Aldrovanda is aquatic, and specialised in catching small invertebrates; Dionaea is terrestrial and catches mostly spiders, oddly

The traps are very similar: they have leaves whose terminal section is divided into two lobes, hinged along the midrib. Trigger hairs (three on each lobe in the case of Dionaea, many more in the case of Aldrovanda) inside the trap lobes are sensitive to touch. When the trigger hairs are bent, stretch-gated ion channels in the membranes of cells at the base of the trigger hair open, generating an action potential, which propagates to cells in the midrib cite journal | author=Hodick D, Sievers A | title=The action potential of Dionaea muscipula Ellis | journal=Planta | volume=174 | year=1989 | pages=8-18 | url = http://www.springerlink.com/index/KL80VV1327508844.pdf | id = . These cells respond by
pumping out ions, which may either cause water to follow by osmosis (collapsing the cells in the midrib) or cause rapid acid growth cite journal | author=Hodick D, Sievers A | title=On the mechanism of closure of Venus flytrap (Dionaea muscipula Ellis) | journal=Planta | volume=179 | year=1988 | pages=32-42 | url = http://www.springerlink.com/index/QPK061437U675H10.pdf | id = (the mechanism is still debated). Whatever the initial mechanism, changes in the shape of cells in the midrib
allow the lobes (which are held under tension) to snap shut , flipping rapidly from convex to concave cite journal | author=Forterre Y, Skotheim JM, Dumais J, Mahadevan L | title=How the Venus flytrap snaps | journal=Nature | volume=433 | issue=7024 | year=2005 | pages=421-5 | url = http://www.nature.com/nature/journal/v433/n7024/abs/nature03185.html | id = and interring the prey item. This whole process takes less than
a second. In the Venus flytrap, spurious closure (in response to raindrops and blown-in debris)
is prevented by the leaf's having a simple memory: for the lobes to shut, two stimuli are
required, between 0.5 and 30 seconds apart.

The snapping of the leaves is a case of thigmonasty (undirected movement in response to touch). Further stimulation of the
lobe's internal surfaces by the struggling insects causes the lobes to grow together (towards the prey: thigmotropism),
sealing the lobes hermetically, and forming a stomach in which digestion occurs over
a period of one to two weeks. Leaves can be reused three or four times before
they become unresponsive to stimulation.

Bladder traps

thumb|200px|left|[Utricularia: illustration showing bladder traps]

Bladder traps are exclusive to the genus Utricularia, or bladderworts.
These possess bladders (vesicula), which pump ions out of their interiors. Water follows the ions by
osmosis, and this generates a partial vacuum inside the bladder. The bladder has a
small opening, sealed by a hinged door. In aquatic species, the door has a pair
of long trigger hairs. Aquatic invertebrates (such as Daphnia) that touch these
hairs deform the door by lever action: this releases the vacuum, and sucks the
invertebrate into the bladder, where it is digested. Many species of Utricularia (such as U. sandersonii) are terrestrial, growing on waterlogged soil, and their trapping mechanism is triggered in a slightly different manner. Bladderworts lack roots, although terrestrial species have anchoring stems that resemble them. Temperate aquatic bladderworts generally die back to a resting turion during the winter months, and U. macrorhiza appears to regulate the number of bladders it bears in response to the prevailing nutrient content of its habitat.

Lobster-pot traps

thumb|200px|right|A [Genlisea flower.
Carnivorous plants still need to attract insects to pollinate their flowers.]

Lobster pots are found in Sarracenia psittacina, and more elegantly, in
Genlisea, the corkscrew plants. In these plants, which appear to
specialise in aquatic protozoa, a Y-shaped modified leaf allows entrance to prey, but not exit.
This is achieved by inward-pointing hairs, which force the prey to move in a particular direction. Prey items entering the spiral entrance that
coils around the upper two arms of the 'Y' are forced to move inexorably towards a 'stomach'
in the lower arm of the 'Y', where they are digested. Prey movement is also thought to be encouraged by water movement through the trap, produced in a similar way to the vacuum in bladder traps, and probably evolutionarily related to it.

Borderline carnivores

To be a fully fledged carnivore, a plant must attract, kill, and digest prey;
and it must benefit from absorbing the products of the digestion (mostly amino acids and ammonium ions). There are a number of plants which fail on one or more
of these counts: whether these count as carnivorous is a matter of definition, although to many horticulturalists, it is a matter of taste. There is a spectrum of carnivory found in plants: from
true 'non-carnivores' like cabbages, through borderline carnivores, through unspecialised and simple traps, like Heliamphora, to extremely specialised and complex traps, like that of the Venus flytrap.

thumb|200px|left|[Roridula: a borderline carnivore that gains nutrients from its 'prey' via the droppings of a predatory bug]

The borderline carnivores of most interest here are Roridula and Catopsis berteroniana. Catopsis is a borderline carnivorous bromeliad, like Brocchinia; however,
Roridula has a more intricate relationship with its 'prey'. The plants in this genus produce sticky leaves
with mucilage-tipped glands, and look extremely similar to some of the larger
sundews. However, they do not directly benefit from the insects they catch. Instead, they
form a mutualistic symbiosis with species of assassin bug (genus Pameridea),
which eat the trapped insects: the plant benefits by absorbing nutrients from the bugs'
faeces.

A number of species in the Martyniaceae (previously the Pedaliaceae), such as Ibicella lutea have sticky leaves that trap insects; however, these plants have not been shown conclusively to be carnivorous. Likewise, the seeds of Shepherd's Purse, urns of Paepalanthus bromelioides, bracts of Passiflora foetida, and flower stalks and sepals of triggerplants (Stylidium) appear to trap and kill insects, but their classification as carnivores is contentious.

The production of specific prey-digesting enzymes (proteases, ribonucleases, phosphatases, etc.), is sometimes used as a diagnostic criterion for carnivory. However, this would probably discount Byblis, Heliamphora and Darlingtonia, all of which appear to rely on the enzymes of symbiotic bacteria to break down their prey, but are generally considered to be acceptable as carnivores. However, discounting the enzyme-based definition leaves open the question of Roridula: there is no clear reason why a plant's possession of symbiotic bacteria that allow it to benefit from trapped prey should allow the plant to be considered carnivorous, whilst possession of symbiotic bugs should not.

Evolution

Studying the evolution of carnivorous plants is made difficult by the paucity of their fossil record. Very few fossils have been found, and all that do exist are either seed or pollen. Carnivorus plants are generally herbs and their traps are made of primary growth: they do not generally form readily fossilisable structures such as thick bark or wood, and even if they did, their traps themselves would probably not be preserved.

However, much can be deduced from the structure of current traps. Pitfall traps are quite clearly derived from rolled leaves. The vascular tissues of Sarracenia show this quite clearly: the keel along the front of the trap contains a mixture of leftward and rightward facing vascular bundles, as would be predicted from the fusion of the edges of an adaxial (stem-facing) leaf surface. Flypapers also show a simple evolutionary gradient from sticky, non-carnivorous leaves, through passive flypapers to active forms. Molecular data show the Dionaea/Aldrovanda clade is closely related to Drosera cite journal | author=Cameron K, Wurdack KJ, Jobson RW | title=Molecular evidence for the common origin of snap-traps among carnivorous plants | journal=American Journal of Botany | volume=89 | year=2002 | pages=1503-1509 | url = , but the traps are sufficiently dissimilar to make the guess that snap-traps derived from very fast-moving flypapers which became less reliant on glue rather speculative.

There are over a quarter of a million species of flowering plants, but of these, only around five hundred are known to be carnivorous. True carnivory has probably evolved independently at least ten times; however, some of these 'independent' groups are probably descended from a recent common ancestor with a predisposition to carnivory. Some groups (the Ericales and Caryophyllales) seem particularly fertile ground for carnivorous preadaptation, although in the former case, this may be more to do with the ecology of the group than its morphology, as most of the members of this group grow in low-nutrient habitats such as heath and bog.

It has been suggested that all of the various trap types are modifications of a similar basic structure - the hairy leafcite book | author=Slack A | title=Carnivorous plants | publisher=Alphabooks | location=London | year=1988 | pages=18-19 | isbn=0713630795
. Hairy (or more specifically, stalked-glandular) leaves have the ability to catch and retain drops of rainwater (especially if shield-shaped or peltate) in which bacteria can breed. Insects that land on the leaf can become mired by the surface tension of the water, and suffocate. The bacteria then begin the process of decay, releasing nutrients from the corpse, which the plant can absorb through its leaves. This foliar feeding can be observed in most non-carnivorous plants. Plants that were better at retaining insects or water therefore had a selective advantage, because they had access to more nutrients than less efficient plants. Rainwater can be retained by cupping the leaf, leading to pitfall traps. Alternatively, insects can be retained by making the leaf stickier by the production of mucilage, leading to flypaper traps.

The pitfall traps may have evolved simply by selection pressure for the production of more deeply cupped leaves, followed by 'zipping up' of the margins and subsequent loss of most of the hairs, except at the bottom, where they help retain prey.

The lobsterpot traps of Genlisea are difficult to interpret: they may have developed from bifurcated pitchers that later specialised on ground dwelling prey; or perhaps from bladder traps whose prey-guiding protrusions became something more substantial than the net-like funnel found in most aquatic bladderworts. Whatever their origin, their helical shape is an adaptation that displays as much trapping surface as possible in all directions when buried in moss.

The traps of the bladderworts may be derived from pitchers that specialised in aquatic prey when flooded, like Sarracenia psittacina does today. Escaping prey items in terrestrial pitchers have to climb or fly out of a trap, and both of these can be prevented by wax, gravity and tube narrowness. However, a flooded trap can be swum out of, so in Utricularia, a one way lid may have developed to form the door of a proto-bladder. Later, this may have become active by the evolution of a partial vacuum inside the bladder, tripped by prey brushing against trigger hairs on the door of the bladder.

Flypaper traps include the various true flypapers and the snap traps of Aldrovanda and Dionaea. The production of sticky mucilage is found in many non-carnivorous genera, so it is not difficult to see how the passive glue traps in Byblis and Drosophyllum evolved.

The active glue traps use rapid plant movements to trap their prey. Rapid plant movement can be due to actual rapid growth, or it can be due to rapid changes in cell turgor, which allow cells to expand or contract by quickly altering their water content. Slow-moving flypapers like Pinguicula exploit growth, but the Venus flytrap uses more rapid turgor changes. In this plant, the movement is so rapid that glue has become unnecessary. The stalked glands that once made it (and are so evident in Drosera) have become the teeth and trigger hairs - an example of natural selection hijacking preexisting structures for new functions.

Recent taxonomic analysis cite journal | author=Cameron KM, Chase MW, Swensen SM | title=Molecular evidence for the relationships of Triphyophyllum and Ancistrocladus | journal=American Journal of Botany | volume=82 | issue=6 | year=1995 | pages=117-118 | url=http://www.jstor.org/view/03636445/di001110/00p0305w/0 http://www.carnivorousplants.org/cpn/samples/Science262Evol.htm Discussion of this paper at the International carnivorous plant society website (original paper requires JSTOR subscription). of the relationships within the Caryophyllales indicate that the Droseraceae, Triphyophyllum, Nepenthaceae and Drosophyllum, whilst closely related, are embedded within a larger clade that includes non-carnivorous groups such as the tamarisks, Ancistrocladaceae, Polygonaceae and Plumbaginaceae. Interestingly, the tamarisks possess specialised salt-excreting glands on their leaves, as do several of the Plumbaginaceae (such as the sea lavender, Limonium), which may have been co-opted for the excretion of other chemical, such as proteases and mucilage. Some of the Plumbaginaceae (e.g. Ceratostigma) also have stalked, vascularised glands that secrete mucilage on their calyces and aid in seed dispersal and possibly in protecting the flowers from crawling parasitic insects. It is not unlikely that these are homologous with the tentacles of the carnivorous genera. It is possible that carnivory evolved from a protective function, rather than a nutritional one.
The balsams (such as Impatiens), which are closely related to the Sarraceniaceae and Roridula similarly possess stalked glands.

The only traps that are unlikely to have descended from a hairy leaf/sepal of some sort are the carnivorous bromeliads (Brocchinia and Catopsis). These plants have just used the urn that is a fundamental part of the structure of a bromeliad for a new purpose, and built on it by the production of wax and the other paraphernalia of carnivory.

Ecology and modelling of carnivory

Carnivorous plants are widespread but rather rare. They are almost entirely restricted to
habitats such as bogs, where soil nutrients are extremely limiting, but where sunlight and water are readily available. Only under such extreme conditions is carnivory favoured to an extent that makes the adaptations obvious.

The archetypal carnivore, the Venus flytrap, grows under quite extreme environmental conditions. The soils in which it grows have nitrate and calcium levels that are almost too low to measure. This poses an obvious problem since nitrogen is essential for protein synthesis and calcium for cell wall stiffening. Soil phosphate and iron levels are also very low, phosphate being essential for nucleic acid synthesis, and iron for chlorophyll synthesis. The soil is often waterlogged, which favours the production of toxic ions such as ammonium, and its pH is an extremely acidic 4 to 5. Ammonium can be used as a source of nitrogen by plants, but its high toxicity means that concentrations high enough to fertilise are also high enough to cause damage.

However, the habitat is warm, sunny, constantly moist, and the plant experiences relatively little competition from low growing Sphagnum moss. This sort of habitat is typical of many carnivorous plants, and carnivores have a popular reputation as bog plants. However, they are also found in very atypical habitats too. Drosophyllum lusitanicum is found around desert edges and Pinguicula valisneriifolia on limestone (calcium rich) cliffs cite journal | author=Zamora R, Gomez JM, Hodar JA | title=Responses of a carnivorous plant to prey and inorganic nutrients in a Mediterranean environment | journal=Oecologia | volume=111 | year=1997 | pages=443-451 . Any model that attempts to explain carnivory must explain both why carnivores are so often restricted to wet, sunny sites, and how can they can survive away from them.

In all the studied cases, carnivory allows plants to grow and reproduce using animals as a source of nitrogen, phosphorus and (possibly) potassium, when the usual sources in the soil are absent or limiting cite journal | author=Thoren LM, Karlsson PS | title=Effects of supplementary feeding on growth and reproduction of three carnivorous plant species in a subarctic environment | journal=Journal of Ecology | volume=86 | year=1998 | pages=501-510 cite journal | author=Hanslin HM, Karlsson PS | title=Nitrogen uptake from prey and substrate as affected by prey capture level and plant reproductive status in four carnivorous plant species | journal=Oecologia | volume=106 | year=1996 | pages=370-375 cite journal | author=Deridder F, Dhondt AA | title=A positive correlation between naturally captured prey, growth and flowering in Drosera intermedia in two contrasting habitats | journal=Belgian Journal of Botany | volume=125 | year=1992 | pages=30-44 . However, there is a spectrum of dependency on animal prey. Pygmy sundews are unable to use nitrate from soil because they lack the necessary enzymes (nitrate reductase in particular cite journal | author=Karlsson PS, Pate JS | title=Contrasting effects of supplementary feeding of insects or mineral nutrients on the growth and nitrogen and phosphorus economy of pygmy species of Drosera | journal=Oecologia | volume=92 | year=1992 | pages=8-13 ), so they are almost entirely dependent on animal prey. Common butterworts (Pinguicula vulgaris) can use inorganic sources of nitrogen better than organic sources, but a mixture of both gives better growth than either alone . European bladderworts seem able to use either source equally well. Animal prey makes up for deficiencies in soil nutrients, but to different extents in different plants.

Plants use their leaves to intercept sunlight. The light energy is used to reduce carbon dioxide from the air with electrons from water, to make sugars (and other biomass), and a waste product, oxygen, in the process of photosynthesis. Leaves also respire, in a very similar way to animals, by burning their biomass to generate chemical energy. This energy is temporarily stored in the form of ATP (adenosine triphosphate), which acts as an energy currency for metabolism in all living things. As a waste product, respiration produces carbon dioxide.

For a plant to grow, it must photosynthesise more than it respires. If a plant respires more than it photosynthesises, then it will eventually burn up all its available biomass, and die. The potential for plant growth is net photosynthesis. Net photosynthesis is the total gross gain of biomass by photosynthesis, minus the biomass lost by respiration. Understanding carnivory requires a cost-benefit analysis of these factors cite journal | author=Givnish TJ, Burkhardt EL, Happel RE, Weintraub JD | title=Carnivory in the bromeliad Brocchinia reducta, with a cost-benefit model for the general restriction of carnivorous plants to sunny, moist, nutrient-poor habitats | journal=American Naturalist | volume=124 | year=1984 | pages=479-497 | url=http://www.jstor.org/view/00030147/di006263/00p0048e/0 (Requires JSTOR subscription).

In carnivorous plants, the leaf is not just used to photosynthesise, but also as a trap. Changing the leaf shape to make it a better trap generally makes it less efficient at photosynthesis. For example, pitchers have to be held upright, so that only their opercula directly intercept light. The plant also has to expend extra energy on non-photosynthetic structures like glands, hairs, glue and digestive enzymescite journal | author=Gallie, D. R. & Chang, S. C. | title=Signal transduction in the carnivorous plant Sarracenia purpurea - regulation of secretory hydrolase expression during development and in response to resources | journal=Plant Physiology| volume=115 | year=1997 | pages=1461-1471 . The energy source for these things is ATP, so the plant has to respire more of its biomass away to keep up with the demand for energy. Hence, a carnivorous plant will have both decreased photosynthesis and increased respiration, making the potential for growth small, and the cost of carnivory high.

The benefits of carnivory are the nitrogen and phosphorus harvested from the prey items. Being carnivorous allows the plant to grow better when the soil contains little nitrate or phosphate. In particular, an increased supply of nitrogen and phosphorus makes photosynthesis more efficient, because photosynthesis depends on the plant being able to synthesise very large amounts of the (nitrogen rich) enzyme Rubisco (ribulose-1,5-bis-phosphate carboxylase/oxygenase), which is the most abundant protein on Earth. The returns of carnivory are therefore more effective photosynthesis.

Clearly some sort of trade-off occurs. It is intuitively clear that the Venus flytrap is more carnivorous than Triphyophyllum peltatum: the former is a full-time moving snap-trap, the second is a part-time, non-moving flypaper. But is the Venus flytrap more carnivorous than a pitcher plant? The energy 'wasted' by the plant in building and fuelling its trap is a suitable measure of the carnivory of the trap.

thumb|400px|center|Modelling carnivory in plants: gross photosynthesis, respiration and net photosynthesis as a function of the plant's investment in carnivorous adaptations. Non-zero optimum carnivory occurs in brightly lit habitats with very limiting soil nutrients.

Using this measure of investment in carnivory, a model can be proposed . Above is a graph of carbon dioxide uptake (potential for growth) against trap respiration (investment in carnivory) for a leaf in a sunny habitat containing no soil nutrients at all. Respiration is a straight line sloping down under the horizontal axis (respiration produces carbon dioxide). Gross photosynthesis is a curved line above the horizontal axis: as investment increases, so too does the photosynthesis of the trap, because the leaf is receiving a better supply of nitrogen and phosphorus. However, this payoff does not last indefinitely. Eventually some other factor (such as light intensity or carbon dioxide concentration) will become more limiting to photosynthesis than nitrogen or phosphorus supply. As a result, increasing the investment will not make the plant grow any better. The net uptake of carbon dioxide, and therefore the plant's potential for growth, must be positive for the plant to survive. There is a broad span of investment
where this is the case, and there is also a non-zero optimum. Plants investing more or less than this optimum will be taking up less carbon dioxide than an optimal plant, and hence growing less well. These plants will be at a selective disadvantage. At zero investment the growth is zero, because a non-carnivorous plant cannot survive in a habitat with absolutely no soil borne nutrients. No real habitat is this stressful, so non-carnivores can survive in the same habitats as carnivores. In particular, Sphagnum is able to absorb the tiny amounts of nitrates and phosphates contained in rain very efficiently, and also forms symbioses with diazotrophic cyanobacteria.

thumb|400px|center|Modelling carnivory in plants: gross photosynthesis, respiration and net photosynthesis as a function of the plant's investment in carnivorous adaptations. An optimum carnivory of zero occurs in poorly lit habitats with abundant soil nutrients.

In a habitat with abundant soil nutrients but little light (as shown above), the gross photosynthesis curve will be lower and flatter, because light will be more limiting than nutrients. A plant can grow at zero investment in carnivory; however, this is also the optimum investment for a plant, as any investment in traps reduces net photosynthesis (growth) to less than the net photosynthesis of a plant that obtains its nutrients from soil alone.

Carnivorous plants exist between these two extremes: the less limiting light and water are, and the more limiting soil nutrients are, the higher the optimum investment in carnivory, and hence the more obvious the adaptations will be to the casual observer.

The most obvious evidence for this model is that carnivorous plants tend to grow in habitats where water and light are abundant, and where competition is relatively low: the typical bog. Those that do not tend to be even more fastidious in some other way: Drosophyllum lusitanicum grows where there is little water, but it is even more extreme in its requirement for bright light and low disturbance than most other carnivores. Pinguicula valisneriifolia grows on soils with high levels of calcium, but requires strong illumination and lower competition than many butterworts.cite journal | author=Zamora R, Gomez JM, Hodar JA | title=Fitness responses of a carnivorous plant in contrasting ecological scenarios | journal=Ecology | volume=79 | year=1988 | pages=1630-1644

In general, carnivorous plants are poor competitors, because they invest too heavily in structures that have no selective advantage in nutrient-rich habitats. They survive because they can put up with nutrient stresses much higher than non-carnivorous plants can: they succeed because other plants fail. Carnivores are to nutrients what cactuses are to water. Carnivory only pays off when the nutrient stress is high and (particularly) where light is abundant cite journal | author=Brewer JS | title=Why don't carnivorous pitcher plants compete with non-carnivorous plants for nutrients? | journal=Ecology | volume=84 | issue=2 | year=2002 | pages=451-462 | url=http://www.esajournals.org/esaonline/?request=get-document&issn=0012-9658&volume=084&issue=02&page=0451 . When these conditions are not met, some plants give up carnivory temporarily. Sarracenia spp. produce flat, non-carnivorous leaves (phyllodes) in winter. Light levels are lower than in summer, so light is more limiting than nutrients, and carnivory does not pay. The lack of insects in winter exacerbates the problem. Damage to growing pitcher leaves will prevent them from forming proper pitchers, and again, the plant produces a phyllode instead: the production of an inefficient, damaged trap is not worth the energy.

Many other carnivores shut down in some season: tuberous sundews die back to tubers in the dry season, bladderworts die back to turions in winter, and non-carnivorous leaves are made by most butterworts and Cephalotus in the less favourable seasons. Utricularia macrorhiza varies the number of bladders its produces based on the expected density of prey items cite journal | author=Knight SE, Frost TM | title=Bladder control in Utricularia macrorhiza - lake-specific variation in plant investment in carnivory | journal=Ecology | volume=72 | year=1991 | pages=728-734 . Part-time carnivory in Triphyophyllum peltatum may be due to an unusually high need for potassium at a certain point in the life cycle, just before flowering.

The more carnivorous a plant is, the more conventional its habitat is likely to be. Venus flytraps live in a very stereotypical, and very specialised habitat, whereas less carnivorous plants (Byblis, Pinguicula) are found in more unusual habitats (i.e. those typical for non-carnivores). Byblis and Drosophyllum both come from relatively arid regions, and are both passive flypapers, which is arguably the lowest maintenance form of trap. Venus flytraps filter their prey using the teeth around the trap's edge, so that energy is not wasted on prey items that cost more to digest than they pay back. In any evolutionary situation, being as lazy as possible pays, because energy can be devoted to reproduction, and as far as evolution is concerned, short term benefits in reproduction will always outweigh long-term benefits in anything else.

Carnivory very rarely pays: even "carnivorous plants" avoid it when there is too little light, or an easier source of nutrients, and they use as few carnivorous features as are required at a given time or for a given prey item. There are very few habitats stressful enough to make using biomass to make trigger hairs and enzymes worthwhile. Many plants occasionally benefit from animal protein rotting on their leaves, but carnivory obvious enough for the casual observer to notice is rare.

Bromeliads seem very well preadapted to carnivory, but only one or two species can be classified as truly carnivorous. By their very shape, bromeliads will benefit from increased prey-derived nutrient input. In this sense, bromeliads are probably carnivorous; but their habitats are too dark for more extreme, recognisable carnivory to evolve. Most bromeliads are epiphytes, and most epiphytes grow in partial shade on tree branches. Brocchinia reducta, on the other hand, is a ground dweller.

Classification

see also|List of carnivorous

The classification of all flowering plants is currently in a state of flux. In
the Cronquist system, the Droseraceae and Nepenthaceae were placed in the order
Nepenthales, based on the radial symmetry of their flowers, and their possession
of insect-traps. The Sarraceniaceae was placed either in the Nepenthales, or
in its own order, the Sarraceniales. The Byblidaceae, Cephalotaceae, and Roridulaceae
were placed in the Saxifragales; and the Lentibulariaceae in the Scrophulariales (now subsumed
into the Lamialescite journal | author=Muller K, Borsch T, Legendre L, Porembski S, Theisen I, Barthlott W | title=Evolution of carnivory in Lentibulariaceae and the Lamiales | journal=Plant Biology (Stuttgart) | volume=6 | year=2004 | pages=477-490 | url=http://www.thieme-connect.com/DOI/DOI?10.1055/s-2004-817909 ).

In more modern classification, such as that of the Angiosperm Phylogeny Group, the
families have been retained, but they have been redistributed amongst several disparate
orders. It is also recommended that Drosophyllum be considered in a monotypic family outside the rest of the Droseraceae, probably more closely allied to the Dioncophyllaceae. The current recommendations are shown below (only carnivorous genera are
listed):

Dicots

*Asterales (sunflower and daisy order)
**Stylidiaceae
***Stylidium (trigger plants, a borderline carnivore)
*Caryophyllales, (carnation order)
**Dioncophyllaceae
***Triphyophyllum (a tropical liana)
**Drosophyllaceae
***Drosophyllum (Portuguese dewy pine)
**Droseracaeae, (sundew family)
***Aldrovanda (waterwheel plant)
*** Dionaea (Venus flytrap)
***Drosera (sundews)
**Nepenthaceae (tropical pitcher-plant family)
***Nepenthes (tropical pitcher plants or monkey-cups, including Anurosperma)

*Ericales (heather order)
**Roridulaceae
***Roridula (a borderline carnivore)
**Sarraceniaceae (trumpet pitcher family)
***Sarracenia (North American trumpet pitchers)
***Darlingtonia (cobra plant/lily)
***Heliamphora (sun or marsh pitchers)

*Lamiales (mint order)
**Byblidaceae
***Byblis (rainbow plants)
**Lentibulariaceae (bladderwort family)
***Pinguicula (butterworts)
***Genlisea (corkscrew plant)
***Utricularia (bladderworts, including Polypompholyx, the fairy aprons or pink petticoats and Biovularia an obsolete genus)
**Martyniaceae (all borderline carnivores, related to the sesame plant)
***Ibicella
*Oxalidales (wood sorrel order)
**Cephalotus (Albany pitcher plant)

Monocots

*Poales (grass order)
**Bromeliaceae (bromeliad or pineapple family)
***Brocchinia (a terrestrial bromeliad)
***Catopsis (a borderline carnivore)
**Eriocaulaceae (pipewort family)
***Paepalanthus (a borderline carnivore)

Cultivation

Although different species of carnivorous plants have different requirements
in terms of sunlight, humidity, soil moisture, etc., there are commonalities.

Most carnivorous plants require rain water, or water that has been
distilled, deionised by reverse osmosis, or acidified to around pH 6.5 using sulfuric acid.
Common tap or drinking water contains minerals (particularly calcium salts)
that will quickly build up and kill the plant. This is because most carnivorous plants have
evolved in nutrient-poor, acidic soils and are consequently extreme calcifuges. They are therefore very sensitive to excessive soil-borne nutrients. Since most of these plants are found in bogs, almost all are very intolerant of drying. There are exceptions:
tuberous sundews require a dry (summer) dormancy period, and Drosophyllum
requires much drier conditions than most.

Outdoor-grown carnivorous plants generally catch more than enough insects to
keep themselves properly fed. Insects may be fed to the plants by hand
to supplement their diet; however, carnivorous plants are generally unable to
digest large non-insect food items; bits of hamburger, for example, will simply rot,
and this may cause the trap, or even the whole plant, to die.
A carnivorous plant that catches no insects at all will rarely die, although its growth may be
impaired. In general, these plants are best left to their own devices: after underwatering with
tap-water, the most common cause of Venus flytrap death is prodding the traps to watch them
close and feeding them cheese and other inappropriate items.

Most carnivorous plants require bright light, and most will look better under such conditions,
as this encourages them to synthesise red and purple anthocyanin pigments. Nepenthes and
Pinguicula will do better out of full sun, but most other species are happy in
direct sunlight.

Carnivores mostly live in bogs, and those that do not are generally tropical. Hence,
most require high humidity. On a small scale, this can be achieved by placing the
plant in a wide saucer containing pebbles that are kept permanently wet. Small Nepenthes
species grow well in large terraria.

Many carnivores are native to cold temperate regions and can be grown outside in a bog garden year-round.
Most Sarracenia can tolerate temperatures well below freezing despite most species being native to the
southeastern United States. Species of Drosera and Pinguicula also tolerate subfreezing temperatures.
Nepenthes species, which are tropical, require temperatures from 20 to 30°C to thrive.

Carnivorous plants require appropriate nutrient-poor soil. Most appreciate
a 3:1 mixture of Sphagnum peat to sharp horticultural sand (coir is an acceptable, and more ecofriendly
substitute for peat). Nepenthes will grow in orchid compost, or in pure Sphagnum moss.

Ironically, carnivorous plants are themselves susceptible to infestation by
parasites such as aphids or mealybugs. Although small infestations
can be removed by hand, larger infestations necessitate use of an insecticide.
Isopropyl alcohol (rubbing alcohol) is effective as a topical insecticide, particularly on scale insects.
Diazinon is an excellent systemic insecticide that is tolerated by most carnivorous plants.
Malathion and Acephate (Orthene) have also been reported as tolerable by carnivorous plants.

Although insects can be a problem, by far the biggest killer of carnivorous plants
(besides human maltreatment) is grey mould (Botrytis cinerea). This thrives under warm,
humid conditions, and can be a real problem in winter. To some extent, temperate carnivorous plants can
be protected from this pathogen by ensuring that they are kept cool and well ventilated in winter, and that any
dead leaves are removed promptly. If this fails, a fungicide is in order.

The easiest carnivorous plants for beginners are those from the cool temperate zone. These
plants will do well under cool greenhouse conditions (minimum 5°C in winter, maximum 25°C in summer)
if kept in wide trays of acidified or rain water during summer, and kept moist during winter:

*Drosera capensis, the Cape sundew: attractive strap-leaved sundew, pink flowers, very tolerant of maltreatment.
*Drosera binata, the fork-leaved sundew: large, Y-shaped leaves.
*Sarracenia flava, the yellow trumpet pitcher: yellow, attractively veined leaves, yellow flowers in spring.
*Pingicula grandiflora, the common butterwort: purple flowers in spring, hibernates as a bud (hibernaculum) in winter. Fully hardy.
*Pinguicula moranensis, the Mexican butterwort: pink flowers, non-carnivorous leaves in winter.

Venus flytraps will do well under these conditions, but are actually rather difficult to grow: even if treated well, they
will often succumb to grey mould in winter unless well ventilated. Some of the lowland Nepenthes are
very easy to grow, as long as they are provided with relatively constant, hot and humid conditions.

Popular culture

right|thumb|Audrey Junior, the man-eating plant from the [cult film The Little Shop of Horrors]

Carnivorous plants have long been the subject of popular interest and exposition, much of it highly inaccurate. A fanciful carnivorous plant called Audrey Junior (not to be confused with the musical's Audrey II) with an insatiable appetite was the central theme of the 1960 black comedy The Little Shop of Horrors.

Cartoons frequently make use of monstrous plants; examples include, but certainly are not limited to Inspector Gadget, Darkwing Duck, The Simpsons and Zetsu, a villain character in the manga series, Naruto.

The triffids presented in John Wyndham's book, The Day of the Triffids, are plants which can uproot themselves, move, and can kill with a poisonous, whip-like tail. The book leaves open the question of whether the triffids are intelligent.

In Life of Pi by Yann Martel, Pi encounters an island of algae which he later discovers to be carnivorous.

A large plant consumed a young woman in Madagascar in 1878, as witnessed by Dr Carl Liche, or so he reported in the September 26 1920 issue of The American Weekly. The woman was supposed to have been a member of the Mkodos, a 'little known but cruel tribe'. The woman was pictured in an accompanying artwork. In 1925 the same paper offered another carnivorous plant story, of a tree species on Mindanao, in the Philippines. There is no evidence that either of these plants is more than a fanciful story.
left|thumb|Super Mario Bros., where Mario encounters the first Piranha Plant in World 1-2.">[Piranha Plants originally appeared In Super Mario Bros., where Mario encounters the first Piranha Plant in World 1-2.]
Nintendo's Super Mario video games feature the Piranha Plant, a Venus fly trap-like enemy. They are almost always portrayed as a leafy green stalk topped with a white-spotted green or red globe, almost bisected by a toothy white mouth.

The movie Minority Report features a greenhouse full of Sarracenia and Nepenthes in one scene.

Some plants in the Edanna Age of the computer game Myst III: Exile are able to trap animals. One of the puzzles that need to be solved in order to win the game involves setting a bird-like creature free from a plant that resembles the trap found in the Nepenthes genus.

A generic species of pitcher plant appears in the The Elder Scrolls IV: Oblivion. Unlike similar plants, however, it does not produce harvestable ingredients. The reasons for this, and the presence of plants with no purpose in the game, are unclear.

In the computer game expansion: Age of Mythology: The Titans, there is a myth unit that can be summoned called Carnivora which is a carnivorous plant resembling a giant Venus Flytrap that attacks with tentacle-like vines and can ensnare and eat prey as big as a horse. An aquatic version of it can also be summoned.

In the MMORPG World of Warcraft, there are Carnivorous Plant enemies called Lashers. They have a tall stalk with a toothed, flower-like bulb at the end, move on a mess of roots and vines beneath them, and attack with two whip-like vines which grow directly from their main stalk and are almost like arms. They are mostly found in the prehistoric jungle themed area, Un'Goro Crater, but can be found in a few instances, including Maraudon and the Wailing Caverns. Various other Carnivorous Plants feature in other MMORPGs.

In the Deltora Quest book series by Emilly Rhoda, Carnivorous Plants called Grippers are present. They resemble toothed mouths growing in the ground, and are covered with cabbage like leaves which open up to let prey fall in when stepped on. They are dangerous to Humans.