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Insectivorous Plants: Definition with Examples

Insectivorous or Carnivorous Plants

Insectivorous plants: 
» Carnivorous 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
» Because insects are one of the most common prey items for most carnivorous plants, they are sometimes called insectivorous plants.
» Insectivorous Plants is a book by British naturalist and evolutionary theory pioneer Charles Darwin, first published on 2 July 1875 in London.
» Insectivorous plants have adapted to grow in places like swamps and rocky areas where the soil does not have all the nutrients specially nitrogen.
» Insectivorous plants receive nitrogen from its prey.
» Insectivorous plants can obtain water and at least some minerals from the soil, they also extract nutrients from captured animals.
» The process of nutrition by which these plants take in insects and digest the protein part within the body with the help of certain plants is called insectivorous nutrition.
» There are more than 600 species of insectivorous plants, mostly found in North America.
» In India. insectivorous plants are found in Sikkim, Arunachal Pradesh, West Bengal and the Garhwal Himalayas.
» Insectivorous plants can broadly be divided into active and passive types based on their method of trapping their prey.
1.       Active: Use rapid movement (ex. Venus fly- trap, Utricularia)
2.      Passive: sticky hairs or a long tube with hairs that trap prey
» The active ones can close their leaf traps the moment insects land on them.
» The passive plants have a ‘pitfall’ mechanism, having some kind of jar or pitcher-like structure into which the insect slips and falls, to eventually be digested.

Trapping Mechanisms in Insectivorous Plants

» Five basic trapping mechanisms are found in carnivorous plants.
1.  Pitfall traps (pitcher plants) trap prey in a rolled leaf that contains a pool of digestive enzymes or bacteria. Eg.-Pitcher plant, Nepenthes etc.
 
The primitive pitchers of Heliamphora chimantensis are an example of pitfall traps.

2. Flypaper traps use a sticky mucilage. Fly Paper traps are coated with a sticky substance called “mucilage". When an insect lands on the plant it sticks to it, after a while the plant will curl around it and digest it. Eg.-Sundews, Butterworts etc

Sticky glands and tentacle movement on Drosera capensis

3. Snap traps utilize rapid leaf movements. (Venus fly trap) Venus Fly Trap has small trigger hairs on the inside, so if an insect lands on it and triggers only one hair and flies off its lucky but if it triggers more than one it will cause its own doom. Eg.- Venus flytrap, Waterwheel etc.
 
The Venus flytrap: shows reaction to the second touch.

4. Bladder traps suck in prey with a bladder that generates an internal vacuum. (Bladderwort)The Bladderwort is like an under water Venus FlyTrap. The bladders suck in and trap water insects.
The tip of one stolon of Utricularia vulgaris, showing stolon, branching leaf-shoots, and transparent bladder traps 

5. Lobster traps, also known as eel traps, force prey to move towards a digestive organ with inward-pointing hairs. A lobster-pot trap is a chamber that is 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.  Eg.- Corkskrew
Genlisea violacea traps and leaves 

Insectivorous Plants in India

» Insectivorous plants of India belong mainly to three families: Droseraceae, Nepenthaceae and Lentibulariaceae. Droseraceae
1.  Droseraceae (3 species)
2. Nepenthaceae (1 species) and
3. Lentibulariaceae (36 species).

Droseraceae
» Droseraceae is a family of flowering plants. The family is also known as the sundew family.
» It is a small family of carnivorous plants, which consist of approximately 180 species in three extant genera.
» Drosera and Aldrovanda belong to family Droseraceae.
» Most of the members of Droseraceae are contained in Drosera, the true sundews.
» Both Dionaea and Aldrovanda have only one extant species. Droseras secrete a sticky substance from their leaves that traps prey.
» Dionaea and Aldrovanda both use snap-traps that close rapidly when the leaves are disturbed, Dionaea is terrestrial, while Aldrovanda is strictly aquatic.
» Like carnivorous plants of other families, the Droseraceae are able to supplement their nutrient intake, especially that of nitrogen, by capturing and digesting small animals such as insects.
» In this way, these plants are able to thrive in nutrient-deficient areas, such as sphagnum bogs.
» Aldrovanda is a free-floating, rootless aquatic plant, the only species found in India, occurs in the salt marshes of Sunderbans, south of Calcutta. It also grows in fresh water bodies like ponds, tanks and lakes.

Nepenthes
» Nepenthes, also known as tropical pitcher plants, is a genus of carnivorous plants in the monotypic family Nepenthaceae.
» The genus comprises roughly 150 species, and numerous natural and many cultivated hybrids.
» They are mostly liana-forming plants of the Old World tropics, ranging from South ChinaIndonesiaMalaysia and the Philippines; westward to Madagascar (two species) and the Seychelles (one); southward to Australia (three) and New Caledonia (one); and northward to India (one) and Sri Lanka (one).
» The greatest diversity occurs on BorneoSumatra, and the Philippines, with many endemic species.
» Many are plants of hot, humid, lowland areas, but the majority are tropical montane plants, receiving warm days but cool to cold, humid nights year round.
» A few are considered tropical alpine, with cool days and nights near freezing.
» The name "monkey cups" refers to the fact that monkeys have been observed drinking rainwater from these plants.
» Nepenthes has some Ethnomedical uses. In local medicine, the pitchers, along with the debris of trapped insects inside, are rubbed into a paste, mixed with water, and given to cholera patients. The liquid inside the pitcher is consumed as a remedy for urinary troubles; it is also used as eye drops for treating redness and itching of eyes.
» These plants are mainly found in high rainfall hills and plateaus of north-eastern region, at altitudes ranging from 100 —1500 m, particularly in Garo, Khasi and Jaintia hills of Meghalaya.

Lentibulariaceae
» Lentibulariaceae, the bladderwort family, is a family of carnivorous plants containing three genera: Genlisea, the corkscrew plants; Pinguicula, the butterworts; and Utricularia, the bladderworts.
» The Bladderworts generally inhabit freshwater wetlands and waterlogged areas
» The genera Polypompholyx (two species of pink petticoats or fairy aprons) and Biovularia used to be regarded as fourth and fifth members of this family.
» Biovularia has been subsumed into Utricularia, and Polypompholyx has been relegated to a subgenus of Utricularia.
» Placement of the family used to be in the Scrophulariales, which has been merged with Lamiales in the Angiosperm Phylogeny Group system.
» Pinguicula or Butterwort grows in the alpine heights of Himalayas, from Kashmir to Sikkim, along streamsides in cool boggy places.

Conservation of Insectivorous Plants

» Over half of the carnivorous plant species assessed by the International Union for the Conservation of Nature (IUCN) are listed as threatened (i.e. vulnerable, endangered, or critically endangered).
» In India, species like Drosera peltata, Aldrovanda vesiculosa and Nepenthes khasiana have been included in the Red Data Book as endangered plants.
Their popularity with gardeners and traders of medicinal plants is one of the main causes for their decline.

Frequently asked questions on Insectivorous Plants:

What are the 4 traits of a carnivorous plant?
They attract, capture, kill and digest animals
Where in the world can you find these plants?
Everywhere except Antarctica
What is the most common habitat of carnivorous plants?
Nutrient poor wetlands.
What feature of their habitat allowed them to evolve carnivory?
The lack of nutrients available in the soil.
Why does the habitat have this feature?
pH of water is low, so bacteria cannot help decompose plants and plants cannot take up nutrients as easily.
What do carnivorous plants commonly eat?
Insects, spiders and aquatic plants eat small animals, fish and mosquito larvae.
What are the two types of traps they use to catch their prey?
Active and passive
Name a variation of each type of trap.
Active: bladderwort (Utricularia), Venus fly trap (Dionaea). Passive: pitcher plant has a pitfall trap; most carnivorous plants have sticky hairs.

See also:

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