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.

The Nepenthes (from Greek: ne = not, penthos = grief, sorrow; named after the ancient drug Nepenthe), popularly known as Tropical Pitcher Plants or Monkey Cups, are a genus of carnivorous plants in the monotypic family Nepenthaceae that comprises roughly 120 species, numerous natural and many cultivated hybrids. They are vine-forming plants of the Old World tropics, ranging from South China, Indonesia, Malaysia and the Philippines; westward to Madagascar (2 species) and the Seychelles (1); southward to Australia (3) and New Caledonia (1); and northward to India (1) and Sri Lanka (1). The greatest diversity occurs on Borneo and Sumatra 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.

The plants usually consist of a shallow root system and a prostrate or climbing stem, often several metres long, and usually 1 cm or less in diameter, although this may be thicker in a few species (e.g. N. bicalcarata). From the stems arise leaf-like expanded petioles, similar to certain Citrus spp., ending in a tendril, which in some species aid in climbing, and at the end of which forms the pitcher, considered the true leaf. The pitcher starts as a small bud and gradually expands to form a globe- or tube-shaped trap.

The trap contains a fluid of the plant's own production, which may be watery or syrupy and is used to drown the prey. Research has shown that this fluid contains viscoelastic biopolymers that may be crucial to the retention of insects within the traps of many species. The trapping efficiency of this fluid remains high, even when significantly diluted by water, as inevitably happens in wet conditions.

The lower part of the trap contains glands which absorb nutrients from captured prey. Along the upper inside part of the trap is a slick waxy coating which makes the escape of its prey nearly impossible. Surrounding the entrance to the trap is a structure called the peristome (the "lip") which is slippery and often quite colorful, attracting prey but offering an unsure footing. Above the peristome is a lid (the operculum): in many species this keeps rain from diluting the fluid within the pitcher, the underside of which may contain nectar glands which attract prey.

Nepenthes usually produce two types of pitchers. Appearing near the base of the plant are the large lower traps, which typically sit on the ground, while the upper pitchers may be smaller, colored differently, and have different features than the lower pitchers. These upper pitchers usually form as the plant reaches maturity and the plant grows taller. To keep the plant steady, the upper pitchers form a loop in the tendril, allowing it to wrap around nearby support. In some species (e.g. N. rafflesiana) different prey may be attracted by different types of pitchers.

Prey usually consists of insects, but the largest species (N. rajah, N. rafflesiana, etc.) may occasionally catch small vertebrates, such as rats and lizards. Flowers occur in racemes or more rarely in panicles with male and female flowers on separate plants. Seed is produced in a four-sided capsule which may contain 10-60 or more seeds, consisting of a central ovary and two wings, one on either side. Seeds are wind distributed.

For More Information: Carnivorous Plants

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