Everything about Carnivorous Plant totally explained
Carnivorous plants (sometimes called
insectivorous plants) are
plants that derive some or most of their
nutrients (but not
energy) from trapping and consuming
animals or
protozoans, typically
insects and other
arthropods. Carnivorous plants appear adapted to grow in places where the soil is thin or poor in nutrients, especially
nitrogen, such as acidic
bogs and rock outcroppings.
Charles Darwin wrote the first well-known treatise on carnivorous plants in 1875.
True carnivory is thought to have evolved in at least 10 separate lineages of plants, and these are now represented by more than a dozen
genera in 5 families. These include about 625 species that attract and trap prey, produce digestive enzymes, and absorb the resulting available nutrients. Additionally, over 300
protocarnivorous plant species in several genera show some but not all these characteristics.
Trapping mechanisms
Five basic trapping mechanisms are found in carnivorous plants.
- Pitfall traps (pitcher plants) trap prey in a rolled leaf that contains a pool of digestive enzymes or bacteria.
- Flypaper traps use a sticky mucilage.
- Snap traps utilize rapid leaf movements.
- Bladder traps suck in prey with a bladder that generates an internal vacuum.
- Lobster-pot traps force prey to move towards a digestive organ with inward pointing hairs.
These traps may be active or passive, depending on whether movement aids the capture of prey. For example,
Triphyophyllum is a passive flypaper that secretes mucilage, but whose leaves don't grow or move in response to prey capture. Meanwhile,
sundews are active flypapers 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 ones are probably those of
Heliamphora, the sun
pitcher plant. In this
genus, the traps are clearly derived
evolutionarily 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 don't overflow. To counteract this problem,
natural selection has favoured the evolution of an overflow, similar to that of a bathroom
sink - a small gap in the zipped-up leaf margins allows excess water to flow out of the pitcher.
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 the
Southeastern United States (with the exception of one species) and
California respectively.
S. purpurea subsp.
purpurea (
the northern pitcher plant) has a more
cosmopolitan distribution, found as far north as
Canada.
Sarracenia is the pitcher plant genus most commonly encountered in cultivation, because it's relatively hardy and easy to grow.
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,
Sarracenia species secrete enzymes such as
proteases and
phosphatases into the digestive fluid at the bottom of the pitcher;
Heliamphora relies on bacterial digestion alone. The 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,
chlorophyll-free patches through which light can penetrate. Insects, mostly ants, enter the chamber via the opening underneath the balloon. Once inside, they 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 that 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 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, 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, providing some protection from raids by freeloading mammals.
The pitfall trap has evolved independently in at least two other groups. The Albany pitcher plant
Cephalotus follicularis is a small pitcher plant from
Western Australia, with
moccasin-like pitchers. The rim of its pitcher's opening (the
peristome)
is particularly pronounced (both secrete
nectar) and provides a thorny overhang to the opening, preventing trapped insects from climbing out. The lining of most pitcher plants is covered in a loose coating of
waxy flakes, which are slippery for insects, prey that 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 prey.
The final carnivore with a pitfall-like trap is the
bromeliad,
Brocchinia reducta. Like most relatives of the
pineapple, the tightly-packed, waxy leaf bases of the strap-like leaves of this species form an
urn. 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 a specialised insect trap, with a loose, waxy lining and a population of digestive bacteria.
Flypaper traps
The flypaper trap is based on a sticky mucilage, or glue. The leaf of flypaper traps is studded with
mucilage-secreting glands, which may 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'), doesn't 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.
The
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 can bend 180° in a minute or so. Sundews are extremely cosmopolitan, and are found on all the continents except the
Antarctic mainland. They are most diverse in
Australia, the home to the large subgroup of pygmy sundews such as
D. pygmaea, and to 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. Its leaves are incapable of rapid movement or growth. Unrelated, but
similar in habit, are the Australian rainbow plants (
Byblis).
Drosophyllum is unusual 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, but in its juvenile phase, the plant is carnivorous. This
may be related to a requirement for specific nutrients for flowering.
Snap traps
The only two active snap traps – the
Venus flytrap (
Dionaea muscipula) and the
waterwheel plant (
Aldrovanda vesiculosa) – are believed to have had a
common ancestor with similar adaptations. Their trapping mechanism has also been described as a 'mouse trap' or 'man trap', based on their shape or rapid movement. However, the term
snap trap is preferred as 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 a variety of arthropods, including spiders.
The traps are very similar, with leaves whose terminal section is divided into two lobes, hinged along the midrib.
Trigger hairs (three on each lobe in
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 that propagates to cells in the midrib. 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. The mechanism is still debated, but in any case, changes in the shape of cells in the midrib
allow the lobes, held under tension, to snap shut, and interring the prey. 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, 0.5 to 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
Bladder traps are exclusive to the genus
Utricularia, or
bladderworts. The bladders (
vesicula) pump
ions out of their interiors. Water follows by
osmosis, generating 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 touch these hairs and deform the door by
lever action, releasing the vacuum. The invertebrate is sucked into the bladder, where it's 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, but 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
A lobster pot trap is a chamber that's easy to enter, and whose exit is either difficult to find or obstructed by inward-pointing bristles. Lobster pots are the trapping mechanism in
Genlisea, the
corkscrew plants. These plants appear to
specialise in aquatic
protozoa. A Y-shaped modified leaf allows prey to enter but not exit. Inward-pointing hairs force the prey to move in a particular direction. Prey 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're 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.
Outside of
Genlisea, features reminiscent of lobster-pot traps can be seen in
Sarracenia psittacina,
Darlingtonia californica, and, some horticulturalists argue,
Nepenthes aristolochioides.
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). In these pitfall traps, prey simply fall into the urn, assisted by the waxy scales located on the rim.
Roridula has a more intricate relationship with its prey. The plants in this genus produce sticky leaves with resin-tipped glands, and look extremely similar to some of the larger sundews. However, they don't 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 from the nutrients in the bugs'
faeces.
A number of species in the
Martyniaceae (previously
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, 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 criterion for carnivory. However, this would probably discount
Heliamphora, and
Darlingtonia, all of which appear to rely on the enzymes of
symbiotic bacteria to break down their prey, but are generally considered as carnivores. However, discounting the enzyme-based definition leaves open the question of
Roridula. There is no 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
The evolution of carnivorous plants is obscured by the paucity of their
fossil record. Very few
fossils have been found, and then usually only as
seed or
pollen. Carnivorus plants are generally herbs and their traps
primary growth. They generally don't form readily fossilisable structures such as thick bark or wood. The traps themselves would probably not be preserved in any case.
Still, much can be deduced from the structure of current traps. Pitfall traps are quite clearly derived from rolled leaves. The vascular tissues of
Sarracenia is a case in point. 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, but the traps are so dissimilar that the theory of their origin -- very fast-moving flypapers became less reliant on glue -- remains rather speculative.
There are over a quarter of a million species of
flowering plants. 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 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 trap types are modifications of a similar basic structure - the hairy leaf. Hairy (or more specifically, stalked-glandular) leaves can catch and retain drops of rainwater, especially if shield-shaped or
peltate, thus promoting bacteria growth. Insects land on the leaf, become mired by the
surface tension of the water, and
suffocate. Bacteria jumpstart
decay, releasing from the
corpse nutrients that 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. 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 the prey-guiding protrusions of bladder traps became more substantial than the net-like funnel found in most aquatic bladderworts. Whatever their origin, the helical shape of the lobsterpot is an adaptation that displays as much trapping surface as possible in all directions when buried in
moss.
The traps of the bladderworts may have derived from pitchers that specialised in aquatic prey when flooded, like
Sarracenia psittacina does today. Escaping prey in terrestrial pitchers have to climb or fly out of a trap, and both of these can be prevented by wax, gravity and narrow tubes. 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, and the passive glue traps in
Byblis and
Drosophyllum could easily have evolved.
The active glue traps use
rapid plant movements to trap their prey. Rapid plant movement can result from actual growth, or from 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 such rapid turgor changes that glue became unnecessary. The stalked glands that once made it and which 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
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 (
for example 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. These are probably homologous with the tentacles of the carnivorous genera. Perhaps 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 or sepal are the carnivorous bromeliads (
Brocchinia and
Catopsis). These plants use the urn - a fundamental part of a bromeliad - for a new purpose, and build 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 in soils with almost immeasurable
nitrate and
calcium levels. Plants need nitrogen for protein synthesis, calcium for
cell wall stiffening, phosphate 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 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. Still, carnivores are also found in very atypical habitats.
Drosophyllum lusitanicum is found around desert edges and
Pinguicula valisneriifolia on
limestone (calcium rich) cliffs.
In all the studied cases, carnivory allows plants to grow and reproduce using animals as a source of nitrogen, phosphorus and possibly potassium. However, there's 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). Common butterworts (
Pinguicula vulgaris) can use inorganic sources of nitrogen better than organic sources, but a mixture of both is preferred.
In carnivorous plants, the leaf isn't 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 enzymes. To produce such structures, the plant requires ATP and respires more of its biomass. Hence, a carnivorous plant will have both decreased photosynthesis and increased respiration, making the potential for growth small, and the cost of carnivory high.
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), the most abundant protein on Earth.
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. The energy 'wasted' by the plant in building and fuelling its trap is a suitable measure of the carnivory of the trap.
Using this measure of investment in carnivory, a model can be proposed.
In general, carnivorous plants are poor competitors, because they invest too heavily in structures that have no selective advantage in nutrient-rich habitats. They succeed only where other plants fail. Carnivores are to nutrients what
cacti are to water. Carnivory only pays off when the nutrient stress is high and where light is abundant. 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 doesn't pay. The lack of insects in winter exacerbates the problem. Damage to growing pitcher leaves prevent them from forming proper pitchers, and again, the plant produces a phyllode instead.
Many other carnivores shut down in some season. Tuberous sundews die back to tubers in the dry season, bladderworts 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. 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 (
for example those typical for non-carnivores).
Byblis and
Drosophyllum both come from relatively arid regions, and are both passive flypapers, arguably the lowest maintenance form of trap. Venus flytraps filter their prey using the teeth around the trap's edge, so as not to waste energy on hard-to-digest prey. In evolution, laziness pays, because energy can be used for reproduction, and short term benefits in reproduction will outweigh long-term benefits in anything else.
Carnivory rarely pays, so even carnivorous plants avoid it when there's 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 investing biomass and energy in trigger hairs and enzymes worthwhile. Many plants occasionally benefit from animal protein rotting on their leaves, but carnivory that's 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
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 Lamiales).
In more modern classification, such as that of the
Angiosperm Phylogeny Group, the
families have been retained, but they've 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)
Ericales (heather order)
Lamiales (mint order)
Monocots
Poales (grass order)
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 rainwater, 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 don't 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's 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're 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.
Pinguicula 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, that'll often succumb to grey mould in winter unless well ventilated. Some of the lowland Nepenthes are very easy to grow, as long as they're provided with relatively constant, hot and humid conditions.
Cultural depictions
Carnivorous plants have long been the subject of popular interest and exposition, much of it highly inaccurate. Fictional plants have been featured in a number of books, movies, television series, and video games. Typically, these fictional depictions include exaggerated characteristics, such as enormous size or possession of abilities beyond the realm of reality, and can be viewed as a kind of artistic license. The most famous examples of fictional carnivorous plants in popular culture include the 1960's black comedy The Little Shop of Horrors, the triffids of John Wyndham's The Day of the Triffids, and others. Other movies and television series utilize accurate depictions of carnivorous plants for cinematic purposes.
The earliest known depiction of carnivorous plants in popular culture was a case where a large man-eating tree was reported to have consumed a young woman in Madagascar in 1878, as witnessed by "Dr Carl Liche". Liche reported the events in the South Australian Register in 1881. The woman, pictured in an accompanying artwork, was supposed to have been a member of the Mkodos, a 'little known but cruel tribe'. The account has been debunked as pure myth as it appears Dr Liche, the Mkodos, and the tree were all fabrications.
Further Information
Get more info on 'Carnivorous Plant'.
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