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Carnivorous Plants

Carnivorous Plants

Plants that trap and digest tiny animals have fascinated people for centuries. It was known by 1790 that sundews, pitcher plants, and the Venus's-flytrap could catch insects. This interest led Thomas Jefferson to collect Venus'sflytraps near Charleston, South Carolina, for study. A century later, Charles Darwin referred to the Venus's-flytrap as one of the most wonderful plants in the world. More recently, certain adventurous, twentieth-century Hollywood movies depicted man-eating plants as inhabiting mysterious tropical jungles. Carnivorous plants, in fact, are relatively small and do not live in dark swamps and jungles, and the largest animal ever found trapped in one of the plants was a small rat. Carnivorous plants catch mostly insects, and hence are often referred to as insectivorous plants.

Carnivorous plants are defined as plants that attract, catch, digest, and absorb the body juices of animal prey (referred to as the carnivorous syndrome). The major types of carnivorous plants are sundews, pitcher plants, butterworts, bladderworts, and the unique Venus's-flytrap. More than 150 different types of insects have been identified as victims, but also arachnids (spiders and mites), mollusks (snails and slugs), earthworms, and small vertebrates (small fish, amphibians, reptiles, rodents, and birds) are known to have been caught.

Many different kinds of plants have insect-attracting structures such as colorful leaves and flower parts and produce sweet sugar secretions (like nectar). Others may ensnare and kill small animals using sticky hairs, thorns, cupped leaves, poisonous liquids, or a combination of these tactics. In some cases it is known that the juices of dead animals can be absorbed through the surfaces of plant leaves. However, only true carnivorous plants have the ability to obtain nutrients from animal prey.

It is known that carnivorous plants can survive without catching prey. However, botanists believe that the added nutrition derived from carnivory helps the plants grow faster and produce more seeds, thus allowing the plants to survive better and spread into new areas. In general, carnivorous plants grow in poor soils where nitrogen, phosphorus, and potassium are lacking.

MAJOR CARNIVOROUS PLANT GROUPS
Genus Common Name Number of Species (approximate) Geographical Distribution
Sarracenia Trumpet pitcher plant 10 Southeastern United States, with one species extending across Canada
Darlingtonia California pitcher plant 1 Northern California and adjacent Oregon
Heliamphora South American pitcher plant 5 Venezuela, Guyana, Brazil
Nepenthes Tropical pitcher plant 75 Southeast Asian tropics, from Australia, Malaysia, and India to Madagascar
Cephalotus Australian pitcher plant 1 Western Australia
Drosera Sundew 110 Worldwide, especially South Africa and Australia
Dionaea Venus's-flytrap 1 Southeastern North Carolina and adjacent South Carolina
Pinguicula Butterwort 60 Mostly Northern Hemisphere
Utricularia Bladderwort 200 Worldwide

They obtain these nutrients, especially nitrogen and phosphorus, from their prey, and they are quickly absorbed through the leaf surface and transported throughout the plant. Although carnivorous plants do absorb nutrients from a weak fertilizer, for instance, high concentrations of fertilizer, as are suitable for garden crops and houseplants, normally kill carnivorous plants.

Habitats

There are more than 450 different species of carnivorous plants found in the world. At least some occur on every continent except Antarctica. They are especially numerous in North America, southeastern Asia, and Australia. Carnivorous plants typically live in wet habitats that are open and sunny, with nutrient-poor soils having an acidic pH . They do not like competition from other plants, and thus seem to thrive in the nutrient-poor habitats where other types of plants do not grow very well. These plants may be found in wet meadows in the southeastern United States or in peat-moss bogs in northern North America and Eurasia. Some are true aquatics, growing in the quiet waters of ponds and ditches around the world. Still others grow on wet, seeping, rocky cliffs or moist sand. In many cases they grow in places that have periodic fires that act to cut down on competition, keep their habitats open, and release nutrients into the soil.

Types of Traps

The traps of carnivorous plants are always modified leaves. They may be active or passive in their mechanism. Active traps have sensitive trigger hairs and moving parts, such as the sticky, glue-tipped hairs that cover the leaves of sundews. The paired leaf blades of the Venus's-flytrap snap shut like jaws when trigger hairs are touched inside. The aquatic bladderworts have little inflated pouches that suck in microscopic animals and mosquito larvae. The passive traps of terrestrial butterworts consist of flat leaves covered with a greasy, sticky surface that are effective at catching crawling insects much like flypaper traps flies. The elegant pitcher plants have passive pitfall traps that are hollow, tubular leaves. Insects fall in, die, and sink to the bottom to be digested. The hoods on most pitcher plants keep out rain-water and prevent prey from flying out. In many cases, especially in pitcher plants that hold water, bacteria may aid in digesting prey. It is also known that several species of mites and fly larvae live inside the trumpet leaves of pitcher plants, without themselves being harmed, and help break down prey for digestion. Pitcher plants may be terrestrial, growing in clumps of erect pitcher leaves (such as the Sarracenia pitcher plants) in the North American temperate zone, or they may grow as sprawling vines in the Malaysian tropics, with pitchers hanging from the tips of their flat leaf blades (such as the Nepenthes pitcher plants).

Microscopic glands are present on each type of trap. They are specialized cells that perform various jobs. They may act as receptors to detect the presence of prey, or they may secrete digestive fluids to dissolve the animal bodies with only the outer shell of chitin of arthropods (insects, spiders, and their relatives) remaining undigested. The glands also absorb the products of digestion, taking them into the leaves of the plant. For example, the sticky hairs of the sundew trap the insect and slowly curve over to press the victim onto the leaf surface where digestive juices are secreted and nutrients absorbed.

While a variety of carnivorous plants are scattered around the world, the area with the most numerous types is the Green Swamp Nature Preserve in southeastern North Carolina (Brunswick County). Occurring in this area are four species of Sarracenia, four species of Drosera, ten species of Utricularia, three species of Pinguicula, and the single species of Dionaea.

see also Evolution of Plants; Interactions, Plant-Insect; Peat Bogs; Wetlands.

T. Lawrence Mellichamp

Bibliography

Cheers, Gordon. A Guide to Carnivorous Plants of the World. New York: Collins Publishers, 1992.

D'Amato, Peter. The Savage Garden: Cultivating Carnivorous Plants. Berkeley, CA: TenSpeed Press, 1998.

Lloyd, Francis E. The Carnivorous Plants. First printed in 1942. New York: Dover Publications, 1976.

Schnell, Donald E. Carnivorous Plants of the United States and Canada. Winston-Salem, NC: John F. Blair Publisher, 1976.

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carnivorous plant

carnivorous plant (insectivorous plant) Any plant that supplements its supply of nitrates in conditions of nitrate deficiency by digesting small animals, especially insects. Such plants are adapted in various ways to attract and trap the insects and produce proteolytic enzymes to digest them. Venus' fly trap (Dionaea), for example, has spiny-margined hinged leaves that snap shut on an alighting insect. Sundews (Drosera) trap and digest insects by means of glandular leaves that secrete a sticky substance, and pitcher plants (families Nepenthaceae and Sarraceniaceae) have leaves modified as pitchers into which insects fall, drowning in the water and digestive enzymes at the bottom.

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carnivorous plants

carnivorous plants: see bladderwort; pitcher plant; Venus's-flytrap.

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carnivorous plant

carnivorous plant See insectivorous plant

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Carnivorous plants

Carnivorous plants

Ecology of carnivorous plants

The types of traps

Conservation and protection of carnivorous plants

Resources

Carnivorous plants are botanical oddities that supplement their requirement for nutrients by trapping, killing, and digesting small animals, mostly insects. Carnivorous plants are photosynthetic, and are therefore fundamentally autotrophic. Still, their feeding relationship with animals represents a reversal of the normal trophic connections between autotrophs and consumers.

Carnivorous plants have long been fascinating to humans. They have the subject of some captivating tales of science fiction, involving fantastic trees that consume large, unwary creatures in tropical forests. Tales have even been told about ritual sacrifices of humans to these awesome carnivores, presumably to appease evil, botanical spirits. Fortunately, fact involves much smaller predators than those of science fiction. Still, the few species of carnivorous plants that really exist are very curious variants on the usual form and function of plants. Scaled up, these carnivores would indeed be formidable predators.

All species of carnivorous plants are small, herbaceous plants, generally growing in nutrient poor habitats, such as acidic bogs and oligotrophic lakes. The usual prey of these green predators is not unwary deer, cattle, or humans, but insects and other small invertebrates, although a few of the larger species are capable of capturing tadpoles and small fish.

Ecology of carnivorous plants

Carnivorous plants are mostly herbaceous perennials with poorly developed root systems, and often propagate by vegetative means, such as stolons and rhizomes. Carnivorous plants are typically intolerant of competition, occurring in open, wet habitats subject

to full sunlight. Carnivorous plants are often tolerant of a limited amount of disturbance, and in fact may benefit from a low intensity of trampling, which prepares a substrate suitable for the germination of their seeds and the establishment of new individuals. Some species are also tolerant of light fires, which also favor their reproduction.

Most carnivorous plants grow in acidic bogs, unproductive lakes, or sandy soils. These are all habitats that are poor in the nutrients that plants require for growth, particularly inorganic nitrogen, phosphorus, and calcium. The nutrients obtained through carnivory are important to these plants. In the absence of animal foods these plants grow less well, and they flower sparsely or not at all.

The types of traps

Contrary to some portrayals in science fiction, the flowers of carnivorous plants are not the organs that ensnare their prey. Rather, in all cases the deadly traps are modified leaves and stems. There are three basic types of trapping organs: active, adhesive, and passive.

Active traps of carnivorous plants attract their mostly arthropod prey using various machinations, including color, scent, and nectar. Once a victim is suitably within, the trap rapidly closes, preventing the escape of the prey. The active trap of the Venus fly-trap (Dionaea muscipula ) is modeled on a basic clamshell design. This species utilizes a fast-acting response to a mechanical stimulus caused when an insect triggers sensitive hairs in the trap, causing its clam-shell leaves to close. The fringing outer projectiles of the leaves rapidly enclose to form a barrier that prevents the trapped arthropod from escaping. At the same time, mechanical stimuli from the struggling victim trigger the synthesis and excretion of digestive enzymes onto the inner surface of the trap, which facilitate digestion of the prey.

Another design of active trap is based on a small, hollow chamber with a trap door. This design is utilized by the bladderworts (various species of Utricularia ), small aquatic plants that form little bladders with diameters of several millimeters, that trap tiny aquatic invertebrates behind a rapidly closing trap door. The door of the bladderwort trap initially swings quickly into the bladder, triggered to respond in this way by motion sensed by fine, fringing bristles. The inward motion of the door develops a suction that can sweep invertebrates into the trap, where they are trapped by the re-closing door, and are digested for the nutrients they contain.

Adhesive, semi-active traps primarily rely on sticky, surface exudates to ensnare their prey. Once a victim is firmly entangled, the leaf slowly enfolds to seal the fate of the unlucky arthropod, and to facilitate the process of digestion. This manner of trap is typified by the most species-rich of the carnivorous plants, the genus of plants known as sundews (Drosera spp.). These plants develop relatively wide, modified leaves, that are densely covered with stalked glands that resemble tentacles several millimeters long. Each tentacle is tipped with a droplet of sticky mucilage. Unwary arthropods, lured by scent, color, and nectar, are caught by this gluey material and are then firmly entangled during their struggles. The leaf then slowly, almost imperceptibly, enfolds the prey, which is then digested by proteolytic enzymes secreted by special glands on the leaf surface.

Passive traps lie in deadly wait for their small victims, which are attracted by enticing scents, colors, and nectar. However, these seeming treats are located

at the end of a fatal, usually one-way passage, from which the prey cannot easily exit. The passage terminates in a pit filled with water and digestive enzymes, where the victim drowns, or is attacked by predacious insects that live symbiotically with the carnivorous plant.

The ingenious design of the pitcher plant (Sarracenia purpurea ) is a revealing example of passive traps. The pitcher plant has foliage modified into upright vessels, as much as 4-6 in (10-15 cm) tall. When mature, these are reddish-green in color, with ultraviolet nectar guides pointing into their interior, which also emits alluring scents. The fringing lip and upper part of the inside of the pitcher are rich in insect attracting nectaries (organs that secrete nectar), and are covered with stiff, downward pointing bristles. These bristles can be easily traversed by an insect walking into the trap, but they passively resist movement upwards and out of the trap. Beneath the zone of bristles is a very waxy, slippery zone, the surface of which is almost impossible for even the tiny feet of insects to grasp, so they fall to the bottom of the trap. There the victim encounters a pool of collected rainwater, replete with digestive enzymes and the floating

corpses of drowned insects, in various stages of decay and digestion. The newest victim struggles for a while, then drowns, and is digested.

Interestingly, a few species of insects are capable of living happily in the water-filled vessels of the pitcher plant and related species, such as the cobra plant (Darlingtonia californica ). These insects are resistant to the digestive enzymes of the carnivorous plants, and they utilize the pitchers as a micro-aquatic habitat. Some species of midges and flies that live in pitcher plants actually attack recently trapped insects, killing and feeding on them. Eventually, the carnivorous plant benefits from nutrients excreted by the symbiotic insects. These pitchers also support a rich microbial community, which are useful in the decay of trapped arthropods, helping to make nutrients available for uptake by the carnivorous plant.

Conservation and protection of carnivorous plants

Most species of carnivorous plants are rare, and many are endangered. The principle threats to these species are habitat destruction caused by the drainage and infilling of wetlands and bogs to develop housing, and ecological conversions associated with agriculture and forestry. The mining of bog peat for horticultural materials or as a source of energy is another threat to some species of carnivorous plants. In addition, some species of carnivorous plants are actively collected in the wild to supply the horticultural trade, and this can seriously threaten the populations of those species.

Venus flytrap is a famous North American example of a carnivorous plant that is endangered in the wild. The natural distribution of this species is

Key Terms

Carnivorous plant A plant that supplements its nutrient requirements by trapping, killing, and digesting small animals, most commonly insects.

Oligotrophic Refers to a waterbody or wetland with a restricted supply of nutrients and a small rate of productivity.

restricted to a small area of the coastal plain of North and South Carolina, fringing inland as far as 124 mi (200 km) along about 186 mi (300 km) of the coast, on either side of Cape Fear. However, the Venus flytrap only occurs today in a few small, scattered remnants of its natural habitat, associated with open spots in acidic bogs and pine savannas. To some degree this species has been endangered in the wild by excessive collecting in the past, but the modern threat is mostly associated with habitat losses to urbanization, agriculture, and forestry.

Fortunately, the Venus flytrap and many other species of carnivorous plants are fairly easy to propagate by vegetative means, usually by sowing leaf fragments onto moist sphagnum peat. For these species, there is no need to collect plants from the wild to supply the economic demands of horticulture.

However, some other species of carnivorous plants cannot be easily propagated in greenhouses, and the demand for these species by aficionados of these charismatic carnivores must be satisfied by collecting wild plants. In some cases, these demands are resulting in unsustainable harvests that are endangering wild populations, for example, of some of the species of the tropical Eurasian pitcher plant, Nepenthes.

However, even species that can be propagated in greenhouses may be collected from the wild for sale to horticulturalists, because quick and easy profits can be made in this way. So, if you decide to try to grow carnivorous plants as unusual pets, ensure that you are obtaining stock that was cultivated in a greenhouse, and not collected from the wild.

Resources

BOOKS

Juniper, B.E., R.J. Robins, and D.M. Joel. The Carnivorous Plants. San Diego: Academic Press, 1989.

Bill Freedman

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Carnivorous Plants

Carnivorous plants

Carnivorous plants are botanical oddities that supplement their requirement for nutrients by trapping, killing, and digesting small animals, mostly insects . Carnivorous plants are photosynthetic, and are therefore fundamentally autotrophic. Still, their feeding relationship with animals represents a reversal of the normal trophic connections between autotrophs and consumers.

Carnivorous plants have long been fascinating to humans. They have the subject of some captivating tales of science fiction, involving fantastic trees that consume large, unwary creatures in tropical forests . Tales have even been told about ritual sacrifices of humans to these awesome carnivores, presumably to appease evil, botanical spirits. Fortunately, fact involves much smaller predators than those of science fiction. Still, the few species of carnivorous plants that really exist are very curious variants on the usual form and function of plants. Scaled up, these carnivores would indeed be formidable predators.

All species of carnivorous plants are small, herbaceous plants, generally growing in nutrient poor habitats, such as acidic bogs and oligotrophic lakes. The usual prey of these green predators is not unwary deer , cattle, or humans, but insects and other small invertebrates , although a few of the larger species are capable of capturing tadpoles and small fish .


Ecology of carnivorous plants

Carnivorous plants are mostly herbaceous perennials with poorly developed root systems, and often propagate by vegetative means, such as stolons and rhizomes. Carnivorous plants are typically intolerant of competition, occurring in open, wet habitats subject to full sunlight. Carnivorous plants are often tolerant of a limited amount of disturbance, and in fact may benefit from a low intensity of trampling, which prepares a substrate suitable for the germination of their seeds and the establishment of new individuals. Some species are also tolerant of light fires, which also favor their reproduction.

Most carnivorous plants grow in acidic bogs, unproductive lakes, or sandy soils. These are all habitats that are poor in the nutrients that plants require for growth, particularly inorganic nitrogen , phosphorus , and calcium . The nutrients obtained through carnivory are important to these plants. In the absence of animal foods these plants grow less well, and they flower sparsely or not at all.


The types of traps

Contrary to some portrayals in science fiction, the flowers of carnivorous plants are not the organs that ensnare their prey. Rather, in all cases the deadly traps are modified leaves and stems. There are three basic types of trapping organs: active, adhesive, and passive.

Active traps of carnivorous plants attract their mostly arthropod prey using various machinations, including color , scent, and nectar . Once a victim is suitably within, the trap rapidly closes, preventing the escape of the prey. The active trap of the Venus fly-trap (Dionaea muscipula) is modeled on a basic clamshell design. This species utilizes a fast-acting response to a mechanical stimulus caused when an insect triggers sensitive hairs in the trap, causing its clam-shell leaves to close. The fringing outer projectiles of the leaves rapidly enclose to form a barrier that prevents the trapped arthropod from escaping. At the same time, mechanical stimuli from the struggling victim trigger the synthesis and excretion of digestive enzymes onto the inner surface of the trap, which facilitate digestion of the prey.

Another design of active trap is based on a small, hollow chamber with a trap door. This design is utilized by the bladderworts (various species of Utricularia), small aquatic plants that form little bladders with diameters of several millimeters, that trap tiny aquatic invertebrates behind a rapidly closing trap door. The door of the bladderwort trap initially swings quickly into the bladder, triggered to respond in this way by motion sensed by fine, fringing bristles. The inward motion of the door develops a suction that can sweep invertebrates into the trap, where they are trapped by the re-closing door, and are digested for the nutrients they contain.

Adhesive, semi-active traps primarily rely on sticky, surface exudates to ensnare their prey. Once a victim is firmly entangled, the leaf slowly enfolds to seal the fate of the unlucky arthropod, and to facilitate the process of digestion. This manner of trap is typified by the most species-rich of the carnivorous plants, the genus of plants known as sundews (Drosera spp.). These plants develop relatively wide, modified leaves, that are densely covered with stalked glands that resemble tentacles several millimeters long. Each tentacle is tipped with a droplet of sticky mucilage. Unwary arthropods , lured by scent, color, and nectar, are caught by this gluey material and are then firmly entangled during their struggles. The leaf then slowly, almost imperceptibly, enfolds the prey, which is then digested by proteolytic enzymes secreted by special glands on the leaf surface.

Passive traps lie in deadly wait for their small victims, which are attracted by enticing scents, colors, and nectar. However, these seeming treats are located at the end of a fatal, usually one-way passage, from which the prey cannot easily exit. The passage terminates in a pit filled with water and digestive enzymes, where the victim drowns, or is attacked by predacious insects that live symbiotically with the carnivorous plant .

The ingenious design of the pitcher plant (Sarracenia purpurea) is a revealing example of passive traps. The pitcher plant has foliage modified into upright vessels, as much as 4-6 in (10-15 cm) tall. When mature, these are reddish-green in color, with ultraviolet nectar guides pointing into their interior, which also emits alluring scents. The fringing lip and upper part of the inside of the pitcher are rich in insect attracting nectaries (organs that secrete nectar), and are covered with stiff, downward pointing bristles. These bristles can be easily traversed by an insect walking into the trap, but they passively resist movement upwards and out of the trap. Beneath the zone of bristles is a very waxy, slippery zone, the surface of which is almost impossible for even the tiny feet of insects to grasp, so they fall to the bottom of the trap. There the victim encounters a pool of collected rainwater, replete with digestive enzymes and the floating

corpses of drowned insects, in various stages of decay and digestion. The newest victim struggles for a while, then drowns, and is digested.

Interestingly, a few species of insects are capable of living happily in the water-filled vessels of the pitcher plant and related species, such as the cobra plant (Darlingtonia californica). These insects are resistant to the digestive enzymes of the carnivorous plants, and they utilize the pitchers as a micro-aquatic habitat . Some species of midges and flies that live in pitcher plants actually attack recently trapped insects, killing and feeding on them. Eventually, the carnivorous plant benefits from nutrients excreted by the symbiotic insects. These pitchers also support a rich microbial community, which are useful in the decay of trapped arthropods, helping to make nutrients available for uptake by the carnivorous plant.


Conservation and protection of carnivorous plants

Most species of carnivorous plants are rare, and many are endangered. The principle threats to these species are habitat destruction caused by the drainage and infilling of wetlands and bogs to develop housing, and ecological conversions associated with agriculture and forestry . The mining of bog peat for horticultural materials or as a source of energy is another threat to some species of carnivorous plants. In addition, some species of carnivorous plants are actively collected in the wild to supply the horticultural trade, and this can seriously threaten the populations of those species.

Venus flytrap is a famous North American example of a carnivorous plant that is endangered in the wild. The natural distribution of this species is restricted to a small area of the coastal plain of North and South Carolina, fringing inland as far as 124 mi (200 km) along about 186 mi (300 km) of the coast, on either side of Cape Fear. However, the Venus flytrap only occurs today in a few small, scattered remnants of its natural habitat, associated with open spots in acidic bogs and pine savannas. To some degree this species has been endangered in the wild by excessive collecting in the past, but the modern threat is mostly associated with habitat losses to urbanization, agriculture, and forestry.

Fortunately, the Venus flytrap and many other species of carnivorous plants are fairly easy to propagate by vegetative means, usually by sowing leaf fragments onto moist sphagnum peat. For these species, there is no need to collect plants from the wild to supply the economic demands of horticulture .

However, some other species of carnivorous plants cannot be easily propagated in greenhouses, and the demand for these species by aficionados of these charismatic carnivores must be satisfied by collecting wild plants. In some cases, these demands are resulting in unsustainable harvests that are endangering wild populations, for example, of some of the species of the tropical Eurasian pitcher plant, Nepenthes.

However, even species that can be propagated in greenhouses may be collected from the wild for sale to horticulturalists, because quick and easy profits can be made in this way. So, if you decide to try to grow carnivorous plants as unusual pets, ensure that you are obtaining stock that was cultivated in a greenhouse, and not collected from the wild.


Resources

books

Juniper, B.E., R.J. Robins, and D.M. Joel. The Carnivorous Plants. San Diego: Academic Press, 1989.

Lecoufle, M. Carnivorous Plants: Care and Cultivation. Blandford, U.K.: Sterling Publishing Co., 1991.

Schwartz, R. Carnivorous Plants. New York: Avon Books, 1975.


Bill Freedman

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Carnivorous plant

—A plant that supplements its nutrient requirements by trapping, killing, and digesting small animals, most commonly insects.

Oligotrophic

—Refers to a waterbody or wetland with a restricted supply of nutrients and a small rate of productivity.

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