inner surface of pitcher plant
]]
Pitcher plants are carnivorous plants
known as pitfall traps—a prey-trapping mechanism featuring a deep cavity filled with digestive liquid. The traps of pitcher plant are considered to be "true" pitcher plants and are formed by specialized leaves. The plants attract and drown the prey with nectar.
Types
The term "pitcher plant" generally refers to members of the
Nepenthaceae and
Sarraceniaceae families, but similar pitfall traps are employed by the monotypic
Cephalotaceae and some members of the
Bromeliaceae. The families
Nepenthaceae and
Sarraceniaceae are the most species-rich families of pitcher plants.
Nepenthaceae
The Nepenthaceae contains a single
genus,
Nepenthes, containing over 100 species and numerous hybrids and cultivars. In this genus of
Old World pitcher plants, the pitchers are borne at the end of
that extend from the
midrib of an otherwise unexceptional leaf. Old World pitcher plants are typically characterized as having reduced and symmetrical pitchers with a comprehensive waxy coating on the surface of the inner pitcher wall. The plants themselves are often climbers, accessing the canopy of their habitats using the aforementioned tendrils, although others are found on the ground in forest clearings, or as
on trees.
Sarraceniaceae
The New World pitcher plants (Sarraceniaceae), which comprise three genera, are ground-dwelling herbs whose pitchers arise from a horizontal
rhizome. In this family, the entire leaf forms the pitcher, as opposed to Nepenthaceae, where the pitcher arises from the terminal portion of the leaf. The species of the genus
Heliamphora, which are popularly known as marsh pitchers (or erroneously as sun pitchers), have a simple rolled-leaf pitcher, at the tip of which is a spoon-like structure that secretes nectar. They are restricted to areas of high rainfall in
South America. The
genus
Sarracenia are the trumpet pitchers, which have a more complex trap than
Heliamphora, with an operculum, which prevents excess accumulation of rainwater in most of the species. The single species in the
California genus
Darlingtonia is popularly known as the cobra plant, due to its possession of an inflated "lid" with elegant false-exits, and a forked "tongue", which serves to ferry ants and other prey to the entrance of the pitcher. The species in the genus
Sarracenia readily hybridize, making their classification a complex matter.
The purple pitcher plant, Sarracenia purpurea, is the floral emblem of the province of Newfoundland and Labrador, Canada.
Cephalotaceae
The
Cephalotaceae is a monotypic family with but one genus and species,
Cephalotus. This species has a small (2–5 cm) pitcher similar in form to those of
Nepenthes. Unlike in
Nepenthes, in
Cephalotus follicularis the petiole is attached to the rear of the upper trap rim rather than to the base of the pitcher.
The species occurs in only one location in southwestern
Australia.
Bromeliaceae
A few species of bromeliads (
Bromeliaceae), such as
Brocchinia reducta and
Catopsis berteroniana, are known or suspected to be carnivorous.
Feeding behavior
Attraction
Foraging, flying, or crawling
such as flies are attracted to a cavity formed by the cupped leaf, often by visual lures such as
anthocyanin pigments, and
nectar. Many pitcher plants exhibit patterns of ultraviolet coloration which may play a role in attracting insects.
Some species, such as
Cephalotus follicularis, likely use camouflage to trap insects, as their coloration matches that of the surrounding environment and the plants are often embedded in the substrate such that the traps are flush with the ground.
Olfactory cues can also play a role in attraction. For example, Nepenthes rafflesiana uses flower-scent mimicry to attract insects to its pitchers.
Capture
The rim of the pitcher (peristome) is slippery when moistened by condensation or nectar, causing insects to fall into the trap. The walls of the pitfall may be covered with waxy scales, protruding
aldehyde crystals,
Plant cuticle folds, downward-pointing hairs, or guard-cell-originating cells, to help prevent escape.
The small bodies of liquid contained within the pitcher traps are called
phytotelmata. They drown the insect, whose body is gradually dissolved. This may occur by bacterial action (the bacteria being washed into the pitcher by rainfall), or by digestive
secreted by the plant itself. Pitcher trap fluids largely vary in their viscoelasticity and acidity, which then dictates which type of prey they can target. For example, increased viscoelasticity is associated with increased insect retention to help capture flying insects such as flies, whereas increased fluid acidity can decrease insect killing-time, which can help capture crawling insects such as ants.
Some pitcher plants contain mutualistic insect
, which feed on trapped prey, and whose
excreta the plant absorbs.
Digestion
Whatever the mechanism of digestion, the prey items are converted into a solution of
,
,
,
ammonium and
urea, from which the plant obtains its mineral nutrition (particularly
nitrogen and
phosphorus). Like all carnivorous plants, pitcher plants all grow in locations where the
soil is too poor in minerals and/or too acidic for most plants to survive. Pitcher plants supplement available nutrients and minerals (which plants normally obtain through their roots) with the constituents of their insect prey.
Feces-trapping symbiosis
Mature plants of
Nepenthes lowii attract
(
Tupaia montana), which feed on nectar that the plant produces but also defecate into the pitcher, providing nitrates and other nutrients. The plant and tree shrew have a
symbiosis. The rim of
N. lowii is not slippery so that tree shrews can easily get in and out; it provides more nectar than other pitcher plants. The shape of the pitcher rim and the position of the nectar ensure that the animal's hindquarters are over the rim while it feeds.
[ Pitcher Plant Doubles as Toilet]
Nepenthes rafflesiana var. elongata has a similar relationship with Hardwicke's woolly bats ( Kerivoula hardwickii).
Evolution of the form
It is widely assumed pitfall traps evolved by epiascidiation (infolding of the leaf with the adaxial or upper surface becoming the inside of the pitcher),
with selection pressure favouring more deeply cupped leaves over
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.
See also
-
Darlingtonia State Natural Site – A nature preserve for pitcher plants in Oregon, United States.
-
Baghmara Pitcher Plant Wildlife Sanctuary
Further reading
-
Juniper, B.E., R.J. Robins & D.M. Joel (1989). The Carnivorous Plants. Academic Press, London. ISBN 9780123921703. OCLC 490279526.
-
Schnell, D. (2003). Carnivorous Plants of the United States and Canada. Second Edition. Timber Press, Portland, Ore., ISBN 9780881925401.
External links
