Pitcher plants are carnivorous plants whose prey-trapping mechanism features a deep cavity filled with liquid known as a pitfall trap. It is widely assumed pitfall traps evolved by epiascidiation (infolding of the leaf with the axadial or upper surface becoming the inside of the pitcher), with selection pressure favouring more deeply cupped leaves over evolutionary time. The pitcher trap evolved independently in three eudicot lineages and one monocot lineage, representing a case of convergent evolution. Some pitcher plant families (such as Nepenthaceae) are placed within clades consisting mostly of flypaper traps, indicating that some pitchers may have evolved from the common ancestors of today's flypaper traps by loss of mucilage.
Foraging, flying or crawling insects such as flies are attracted to the cavity formed by the cupped leaf, often by visual lures such as anthocyanin pigments, and nectar bribes. The rim of the pitcher (peristome) is slippery, when moistened by condensation or nectar, causing insects to fall into the trap. Pitcher plants may also contain waxy scales, protruding aldehyde crystals, cuticular folds, downward pointing hairs, or guard-cell-originating lunate cells on the inside of the pitcher to ensure that insects cannot climb out. The small bodies of liquid contained within the pitcher traps are called phytotelmata. They drown the insect, and the body of it is gradually dissolved. This may occur by bacterial action (the bacteria being washed into the pitcher by rainfall) or by enzymes secreted by the plant itself. Furthermore, some pitcher plants contain mutualistic insect larvae, which feed on trapped prey, and whose excreta the plant absorbs. Whatever the mechanism of digestion, the prey items are converted into a solution of amino acids, peptides, phosphates, ammonium and urea, from which the plant obtains its mineral nutrition (particularly nitrogen and phosphorus). Like all carnivorous plants, they grow in locations where the soil is too poor in minerals and/or too acidic for most plants to survive.
Nepenthes (pron.: //), popularly known as tropical pitcher plants or monkey cups, is a genus of carnivorous plants in the monotypic family Nepenthaceae. The genus comprises roughly 140 species, and numerous natural and many cultivated hybrids. They are mostly liana-forming plants of the Old World tropics, ranging from South China, Indonesia, Malaysia 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 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.