Insectivorous Plants of India: Drosera, Pitcher Plant, Utricularia

Insectivorous Plants

• These plants are specialized in trapping insects and are popularly known as insectivorous plants.
• They are very different from normal plants in their mode of nutrition. They, however, never prey upon humans or large animals.
• Insectivorous plants can broadly be divided into active and passive types based on their method of trapping their 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.
• The insectivorous plants often have several attractions such as brilliant colors, sweet secretions and other curios to lure their innocent victims.

Why do they hunt despite having normal roots and photosynthetic leaves?

• These plants are usually associated with rain-washed, nutrient-poor soils, or wet and acidic areas that are ill-drained.
• Such wetlands are acidic due to anaerobic conditions, which cause partial decomposition of organic matter releasing acidic compounds into the surroundings.
• As a result, most microorganisms necessary for complete decomposition of organic matter cannot survive in such poorly oxygenated conditions.
• Normal plants find it difficult to survive in such nutrient poor habitats.
• The hunter plants are successful in such places because they supplement their photosynthetic food production by trapping insects and digesting their nitrogen rich bodies.

Insectivorous plants of India

Insectivorous plants of India belong mainly to three families:

• Droseraceae (3 species),
• Nepenthaceae (1 species) and
• Lentibulariaceae (36 species).

Drosera and Aldrovanda

• Drosera and Aldrovanda belong to family Droseraceae.
• Drosera or Sundew inhabit wet infertile soils or marshy places.
• 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.

Insect trapping mechanism of Drosera

• The tentacles on the leaves secrete a sticky fluid that shines in the sun like dew-drops. Therefore, the Drosera are commonly known as sundews.
• When an insect lured by these glistening drops alights on the leaf surface it gets stuck in this fluid and are absorbed and digested.

Insect trapping mechanism of Aldrovanda

• On the leaf midrib are found some sensitive trigger hairs. The two halves of the leaf blade of Aldrovanda close along the midrib the moment an insect comes into contact with the leaf, trapping the victim inside.

Pitcher Plants Family: Nepenthaceae

• Pitcher plants belong to family nepenthaceae. The members of the family are commonly known as ‘pitcher plants’ because their leaves bear jar-like structures.
• Distribution: Confined to the 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.

Insect trapping mechanism of pitcher plant

• Nepenthes conforms to the pitfall type of trap. A honey like substance is secreted from glands at the entrance of the pitcher. Once the insect enters into the pitcher, it falls down because of the slipperiness.
• The inner wall, towards its lower half, bears numerous glands, which secrete a proteolytic enzyme. This enzyme digests the body of the trapped insects and nutrients are absorbed.

Utricularia and Pinguicula

• Utricularia and Pinguicula belong to family Lentibulariaceae.

Insect trapping mechanism of Utricularia or Bladderworts

• The Bladderworts generally inhabit freshwater wetlands and waterlogged areas.
• Some species are associated with moist moss covered rock surfaces, and damp soils during rains.
• Utricularia in its bladders mouth, has sensitive bristles or hairs. When an insect happens to contact these hairs the door opens, carrying the insect into the bladder along with a little current of water.
• The door is shut when water fills the bladder, the enzymes produced by the inner wall of the bladder digest the insect.

Insect trapping mechanism of Pinguicula or Butterwort

• It grows in the alpine heights of Himalayas, from Kashmir to Sikkim, along stream-sides in cool boggy places.
• In Pinguicula, an entire leaf works as trap. When an insect lands on the leaf surface, it gets stuck in the sticky exudate. the leaf margins roll up thus trapping the victim.

Medicinal Properties of Insectivorous Plants

• Drosera are capable of curdling milk, its bruised leaves are applied on blisters and used for dyeing silk.
• Nepenthes in local medicine to treat cholera patients, the liquid inside the pitcher is useful for urinary troubles, it is also used as eye drops.
• Utricularia is useful against cough, for dressing of wounds, as a remedy for urinary disease.

Threats

• Gardening trading for medicinal properties is one of the main causes for their decline.
• Habitat destruction is also rampant, the wetlands harbouring such plants being the main casualties during the expansion of urban and rural habitation.
• Pollution caused by effluents containing detergents, fertilizers, pesticides, sewage etc. into the wetlands is yet another major cause for their decline (Since insectivorous plants do not tolerate high nutrient levels).
• Moreover, polluted water bodies are dominated by prolific water weeds which cause elimination of the delicate insectivorous plants.