Lindsay Lohan and Carnivorous plant: Difference between pages
(Difference between pages)
Content deleted Content added
m Good idea, but "acceptable" is relative |
TimBentley (talk | contribs) →Ecology and modelling of carnivory: disambiguation link repair (You can help!) |
||
Line 1:
[[
in flower, growing on a road cut in [[Palau]]]]
A '''carnivorous plant''' is a [[plant]] that derives some or most of its
[[nutrient]]s (but not [[energy]]) by trapping and consuming [[animal]]s,
especially [[insect]]s and other [[arthropod]]s. Carnivorous plants usually
grow in places where the soil is thin or poor in nutrients,
especially [[nitrogen]], such as acidic [[bog]]s and rock outcroppings.
[[Charles Darwin]] wrote the first well-known treatise on carnivorous plants in [[1875]].
==Trapping mechanisms==
There are five basic trapping mechanisms that have [[evolution|evolved]] in carnivorous plants. These are:
*Pitfall traps ([[pitcher plant]]s), 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 [[thigmonasty|rapid leaf movements]];
*Bladder traps, which suck in prey with a bladder that generates an internal [[vacuum]];
*Lobster-pot traps, which use inward pointing [[trichome|hairs]] to force prey to move towards a digestive organ.
These traps may also be classified as active or passive. 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
[[sundew]]s, whose leaves undergo rapid growth, aiding in the retention and
digestion of prey.
===Pitfall traps===
Pitfall traps have evolved independently on at least four occasions. The simplest pitfall
traps are probably those of ''[[Heliamphora]]'', the marsh (or sun) [[pitcher plant]].
In this [[genus]], the traps are quite clearly evolutionarily derived from a simple
rolled leaf, whose margins have been 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.
[[image:Heliamphora.jpg|thumb|200px|left|''[[Heliamphora]]'': note the very small [[operculum]] (nectar spoon) ]]
''Heliamphora'' is a member of the [[Sarraceniaceae]], a [[New World]] family in the
order [[Ericales]] ([[heather]]s and allies). ''Heliamphora'' is limited to South America,
but the family contains two other genera, ''[[Sarracenia]]'' and ''[[Darlingtonia (Sarraceniaceae)|Darlingtonia]]'',
which are endemic to [[Florida]] (for the most part) and [[California]] respectively. ''S. purpurea'' (the huntman's cup) has a more cosmopolitan distribution.
''Sarracenia'' is the pitcher plant genus most commonly encountered in cultivation, and its members are most commonly known as trumpet pitchers.
[[image:Darlingtonia californica.jpg|thumb|200px|right|''[[Darlingtonia (Sarraceniaceae)|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 [[protease]]s and [[phosphatase]]s into the digestive
fluid at the bottom of the pitcher; ''Heliamphora'' relies on bacterial digestion alone. These enzymes digest the [[protein]]s and [[nucleic acid]]s in the prey, releasing [[amino acid]]s 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 [[areola]]e, 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 'fangs' (outgrowths of the operculum), which give the plant its name. 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 cup]]s or tropical
pitcher plants of the genus ''[[Nepenthes]]''. In the seventy or so species of this genus,
the pitcher is borne 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.
[[image:Brocchinea.jpg|thumb|200px|left|''[[Brocchinia]]'': a carnivorous bromeliad]]
The pitfall trap has evolved 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 [[wax]]y, 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 [[habitat (ecology)|habitats]] for [[frog]]s, [[insect]]s and (more usefully from the plant's point of view),
[[diazotroph]]ic (nitrogen-fixing) [[bacterium|bacteria]]. In ''Brocchinia'', the urn is specialised as an
insect-trap, with a population of digestive bacteria, and a loose, waxy lining.
<br style="clear:both" />
===Flypaper traps===
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 [[butterwort]]s), or long and mobile (like those of many [[sundew]]s). Flypapers have evolved independently at least five times.
[[image:Pinguiculagrandiflora1web.jpg|thumb|200px|right|''[[Pinguicula]]'': the leaves and even the flower stem are covered in mucilage-secreting glands]]
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 particularly carnivorous. However, this belies the fact that the leaf is an extremely
effective trap of small flying insects (such as [[fungus gnat]]s), and whose surface responds
to prey by relatively rapid growth. This [[thigmotropism|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.
[[image:Regialeaf.jpg|thumb|200px|left|''[[Drosera]]'': detail of moving tentacles]]
The [[sundew]] genus (''[[Drosera]]'') consists of over 100 species of active flypapers, whose
mucilage glands are borne at the end of long [[tentacle]]s, 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 [[Antarctica|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 [[estivation|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 [[Portugal|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 plant|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|Triphyophyllum peltatum]]'', a mamber 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.
<br style="clear:both" />
===Snap traps===
[[image:Aldrovanda1.jpg|thumb|200px|right|''[[Aldrovanda]]'': an aquatic version of the [[Venus flytrap]]]]
There are only two snap-traps, which are believed to have had a similar [[common ancestor]]. These
are the [[Venus flytrap]] (''[[Dionaea muscipula]]'') and the [[waterwheel]] plant (''[[Aldrovanda]] vesiculosa'').
''Aldrovanda'' is aquatic, and specialised in catching small invertebrates; ''Dionaea'' is
terrestrial and catches mostly flies. The traps are very similar: they have leaves whose terminal
section is divided into two lobes, hinged along the midrib. [[Trigger hair]]s (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 channel]]s in the [[membrane]]s of cells at the base of the trigger hair open, generating an
[[action potential]], which propagates to cells in the midrib. These cells respond by
pumping out [[potassium]] ions. Water follows by osmosis, and the cells in the midrib collapse,
allowing the lobes (which are held under tension) to snap shut. 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 [[stimulus|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.
<br style="clear:both" />
===Bladder traps===
[[image:Illustration Utricularia vulgaris0.jpg|thumb|200px|left|''[[Utricularia]]'': illustration showing bladder traps]]
Bladder traps are exclusive to the genus ''[[Utricularia]]'', or ''bladderworts''.
These possess bladders ([[vesiculum|vesicula]]), which pump [[ion]]s 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 [[root]]s, although terrestrial species have anchoring stems that resemble them. Temperate aquatic bladderworts genearlly die back to a resting [[turion]] during the winter months, and ''U. macrorhiza'' appears to regulate the number of bladders its bears in response to the prevailing nutrient content of its habitat.
<br style="clear:both" />
==
[[image:Genlisearepens1web.jpg|thumb|200px|right|''[[Genlisea]]'': carnivorous plants still need to attract insects to pollinate their flowers. Few species deliberately prey on bees]]
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.
<br style="clear:both" />
===Borderline carnivores===
To be a fully fledged carnivore, a plant must attract, kill, and [[digestion|digest]] [[prey]];
and it must benefit from absorbing the products of the digestion (mostly [[amino acid]]s 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.
From this, it should be obvious that there is a spectrum of carnivory: from
'non-carnivores' like [[cabbage]]s, through borderline carnivores, to the
true carnivores, including both unspecialised and simple traps, like ''Heliamphora'', to extremely specialised and complex traps, like that of the Venus flytrap.
[[image:Roridula gorgonias.jpg|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 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 [[mutualism|mutualistic]] [[symbiosis]] with species of [[assassin bug]] (''[[Pameridea]]''),
which eat the trapped insects: the plant benefits by absorbing nutrients from the bugs'
[[feces|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]]'' and bracts of ''[[Passiflora foetida]]'' appear to trap and kill insects, but their classification as carnivores is contentious.
The production of specific prey-digesting enzymes ([[protease]]s, [[ribonuclease]]s, [[phosphatase]]s, ''etc.''), is sometimes used as a diagnostic criterion for carnivory. However, this would probably discount ''[[Byblis (plant)|Byblis]]'', ''Heliamphora'' and ''Darlingtonia (Sarraceniaceae)|Darlingtonia'', all of which appear to rely on the enzymes of [[symbiotic]] [[bacterium|bacteria]] to break down their prey, but are generally considered to be acceptable as carnivores. However, discouting 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 benfit from trapped prey should allow the plant to be considered carnivorous, whilst possession of symbiotic bugs should not.
<br style="clear:both" />
==Evolution==
Elucidating the evolution of carnivorous plants is made difficult by the paucity of their [[fossil record]]. Very few [[fossil]]s have been found, and all that do exist are either [[seed]] or [[pollen]].
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 tissue|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'', 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 plant]]s, 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 [[preadapatation]], 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 leaf. 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 [[suffocation|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'' can be interpreted as pitchers formed from a Y-shaped leaf, that later specialised on ground dwelling prey; or as bladder traps whose prey-guiding protrusions form something more substantial than the net-like funnel found in most aquatic bladderworts. The twist is an adaptation that displays as much trapping surface as possible in all directions when buried in [[moss]]. In this case the hairs were also retained, but to a greater extent, since the trap was no longer held vertically, and could not rely on gravity to keep its prey in.
The traps of the bladderworts are more difficult to explain, but they 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 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 require a little more explanation. 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, and hence is no longer produced. 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 of the relationships within the [[Caryophyllales]] indicate that the [[Droseraceae]], ''[[Triphyophyllum]]'', [[Nepenthaceae]] and ''Drosophyllum'', whilst closely related, are embedded within a larger [[cladistics|clade]] that includes non-carnivorous groups such as the [[Tamarix|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 [[calyx|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: there are only about 500 species,
out of about 250 000 flowering plants. They are almost entirely restricted to
[[habitat (ecology)|habitats]] such as [[bog]]s, where soil nutrients are extremely limiting, but where [[sun|sunlight]] and [[water]] are
readily available. Only under such extreme conditions is carnivory favoured to an extent that
makes the adaptations obvious.
The [[archetype|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 [[waterlogging|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. 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. 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), 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 [[electron]]s from water, to make sugars (and other [[biomass]]), and a waste product, [[oxygen]], in the process of [[photosynthesis]]. Leaves also [[Cellular respiration|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 burnt up by respiration. Understanding carnivory requires a [[cost-benefit analysis]] of these factors.
In carnivorous plants, the leaf is not just used to photosynthesise, but also as a trap. Unfortunately, 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 enzymes. 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.
<br style="clear:both" />
[[image:Carnivorous plant model 1.png|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.]]
<br style="clear:both" />
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 forever. 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 [[cyanobacterium|cyanobacteria]].
<br style="clear:both" />
[[image:Carnivorous plant model 2.png|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.]]
<br style="clear:both" />
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.
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 [[cactus|cacti]] are to water. Carnivory only pays off when the nutrient stress is very high and light is abundant. When these conditions are not met, some plants give up carnivory temporarily. ''Sarracenia'' spp. produce flat, non-carnivorous leaves ([[phyllode]]s) 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 [[turion]]s in winter, and non-carnivorous leaves are made by most butterworts and ''Cephalotus'' in the less favourable seasons. 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 [[stereotype|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 trap form. 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.
The suprising lack of carnivorous bromeliads is instructive here: bromeliads seem very well preadapted to carnivory; however, only one or two species can be classified as truly carnivorous. Most bromeliads are [[epiphyte]]s, and most epiphytes grow in partial shade on [[tree]] branches. It is noteworthy that ''Brocchinia reducta'' is a ground dweller. By their very shape, bromeliads will benefit from increased prey derived nutrient input. In this sense, most bromeliads are probably carnivorous, but their habitats are too dark for more extreme, recognisable carnivory to evolve.
==Classification==
The classification of all [[Angiosperm|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.
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===
*[[Caryophyllales]], ([[carnation]] order)
**[[Dioncophyllaceae]]
***''[[Triphyophyllum]]'', (a [[tropics|tropical]] [[liana]])
**[[Drosophyllaceae]]
***''[[Drosophyllum]]'', (Portuguese dewy pine)
**Droseracaeae, ([[sundew]] family)
***''[[Aldrovanda]]'', (waterwheel plant)
*** ''[[Dionaea]]'', ([[Venus flytrap]])
***''[[Drosera]]'', ([[sundew]]s)
**[[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 (Sarraceniaceae)|Darlingtonia]]'', (cobra plant/lily)
***''[[Heliamphora]]'', (sun or marsh pitchers)
*[[Lamiales]], ([[mint]] order)
**[[Byblidaceae]]
***''[[Byblis (plant)|Byblis]]'', ([[rainbow]] plants)
**[[Lentibulariaceae]], ([[bladderwort]] family)
***''[[Pinguicula]]'', ([[butterwort]]s)
***''[[Genlisea]]'', (corkscrew plant)
***''[[Utricularia]]'', ([[bladderwort]]s, including ''[[Polypompholyx]]'', the fairy aprons or pink petticoats and ''[[Biovularia]]'' an obsolete genus)
**[[Martyniaceae]], (all borderline carvivores, related to the [[sesame]] plant)
***''[[Ibicella lutea|Ibicella]]''
*[[Oxalidales]], ([[wood sorrel]] order)
**''[[Cephalotus]]'', ([[Albany]] pitcher plant)
===Monocots===
*[[Poales]], ([[grass]] order)
**[[Bromeliaceae]], ([[bromeliad]] or [[pineapple]] family)
***''[[Brocchinia reducta|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
[[distill|distilled]], deionised by [[reverse osmosis]], or acidified 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 [[calcifuge|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) [[estivation|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, but its growth will be
impaired. In general, these plant are best left to their own devices: after underwatering with
tap-water, the commonest 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 [[terrarium|terraria]].
Many carnivores are temperate, and although most are intolerant of hard frosts,
many can be kept outside in temperate climates for the majority of the year. The
main exception to this are ''Nepenthes'' sp., which are tropical, and 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 [[mealybug|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.
[[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: beautiful lilac flowers in spring, hibernates as a bud ([[hibernaculum]]) in winter. Fully hardy.
*''[[Pingicula moranensis]]'', the Mexican butterwort: pink flowers, non-carnivorous leaves in winter.
*''[[Darlingtonia californica]]'', the cobra lily: dramatic leaves, purple and lime-green flowers, likes to be watered with large amounts of cooled water during summer.
Venus flytraps will do well under these conditions, but is actually rather difficult to grow: even if treated well, it
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.
==Pop culture==
Carnivorous plants have long been the subject of popular interest and exposition, much of it highly inaccurate.
A fanciful carnivorous plant with an insatiable appetite was the central theme of the comedic play, ''[[Little Shop of Horrors]]'', made from a more serious [[1960]]s movie of the same name.
The [[triffid]]s 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.
The film ''[[Attack of the Killer Tomatoes]]''
is a [[camp]]y movie about [[tomato]]es that for some reason eat people.
It is an intentional spoof on [[1950s|50s]] monster movies.
The [[Pokémon]] [[Victreebel]] is meant to resemble a ''Sarracenia'' while [[Bellsprout]] and [[Weepinbell]] are meant to resemble ''Nepenthes''.
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.
==References==
*Juniper, B. E. ''et al'' (1989) The carnivorous plants. Academic Press Limited.
*Givnish, T. J., Burkhardt, E. L., Happel, R. E. & Weintraub, J. D. (1984). Carnivory in the bromeliad ''Brocchinia reducta'', with a cost-benefit model for the general restriction of carnivorous plants to sunny, moist, nutrient-poor habitats. American Naturalist '''124''' 479-497.
*Brewer, J. S. (1999). Effects of competition, litter, and disturbance on an annual carnivorous plant (''Utricularia juncea''). Plant Ecology '''140''' 159-165.
*Thoren, L. M. & Karlsson, P. S. (1998). Effects of supplementary feeding on growth and reproduction of three carnivorous plant species in a subarctic environment. Journal of Ecology '''86''' 501-510.
*Zamora, R., Gomez, J. M. & Hodar, J. A. (1998). Fitness responses of a carnivorous plant in contrasting ecological scenarios. Ecology '''79''' 1630-1644.
*Gallie, D. R. & Chang, S. C. (1997). Signal transduction in the carnivorous plant ''Sarracenia purpurea'' - regulation of secretory hydrolase expression during development and in response to resources Plant Physiology '''115''' 1461-1471.
*Zamora, R., Gomez, & J. M. Hodar, J. A. (1997). Responses of a carnivorous plant to prey and inorganic nutrients in a Mediterranean environment. Oecologia '''111''' 443-451.
*Hanslin, H. M. & Karlsson, P. S. (1996). Nitrogen uptake from prey and substrate as affected by prey capture level and plant reproductive status in four carnivorous plant species. Oecologia '''106''' 370-375.
*Deridder, F. & Dhondt, A. A. (1992). A positive correlation between naturally captured prey, growth and flowering in ''Drosera intermedia'' in two contrasting habitats. Belgian Journal of Botany '''125''' 33-40.
*Knight, S. E. & Frost, T. M. (1991). Bladder control in ''Utricularia macrorhiza'' - lake-specific variation in plant investment in carnivory. Ecology '''72''' 728-734.
*Cameron, K., Wurdack, K. J. ↦ Jobson, R. W. (2002). Molecular evidence for the common origin of snap-traps among carnivorous plants. American Journal of Botany '''89''' 1503-1509.
*Slack, A. (1986). Insect-eating plants and how to grow them. Alpha Books. Sherborne, UK.
==External links==
{{Commons|Category:Carnivorous plants}}
*[http://www.
*[http://
*[http://www.omnisterra.com/bot/cp_home.cgi Carnivorous Plant Database], provides an up to date, searchable database of all the published species of carnivorous plant
*[http://www.paonline.com/mrmiller/Nurseries.htm Carnivorous Plant Nurseries]
*[http://www.thecarnivorousplantsociety.org/ The Carnivorous Plant Society], has a 24/7 live link with a forum.
*[http://www.thecps.org.uk/ The Carnivorous Plant Society], the UK Carnivorous Plant Society has information on carnivorous plants and tips on cultivation.
*[http://www.carnivorousplants.org/ International Carnivorous Plant Society], provides an extensive [[FAQ]] and links to the Carnivorous Plant Web Ring.
*[http://pages.britishlibrary.net/charles.darwin3/insectivorous/insect01.htm Insectivorous Plants], by Charles Darwin.
*[http://www.jstor.org/view/00030147/di006263/00p0048e/0 Givnish paper on modelling carnivory], requires JSTOR subscription.
* [http://www.carnivorousplants.org/cpn/samples/Science262Evol.htm International carnivorous plant society], discussion of relationships within the [[Caryophyllales]].
* [http://www.carnivorousplants.org/cpn/samples/Science262Byblis.htm International carnivorous plant society], discussion of a simple test for proteases in carnivorous mucilage.
[[Category:
[[Category:
[[
[[
[[de:Fleischfressende Pflanzen]]
[[es:
[[fr:
[[lt:Vabzdžiaėdžiai augalai]]
[[nl:Vleesetende plant]]
[[
[[nn:Kjøtetande plante]]
[[
[[ru:Хищные растения]]
[[
[[
| |||