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Carnivorous Plants / Insectivorous Plants
Carnivorous plants have the most bizarre adaptations to low-nutrient environments. These plants obtain some nutrients by trapping and digesting various invertebrates, and occasionally even small frogs and mammals. Because insects are one of the most common prey items for most carnivorous plants, they are sometimes called insectivorous plants. It is not surprising that the most common habitat for these plants is in bogs and fens, where nutrient concentrations are low but water and sunshine seasonally abundant. As many as thirteen species of carnivorous plants have been found in a single bog (Folkerts, 1982). Most plants absorb nitrogen from the soil through their roots. But carnivorous plants absorb nitrogen from their animal prey through their leaves specially modified as traps.
- the Monkey Cups
As it matures, it suddenly begins inflates with air. Once inflated it begins to fill with liquid, then opens, revealing the enticing interior. The top of the trap has a lid that initially covers the pitcher until growth is complete. When the leaf is fully grown, the lid opens and the trap is ready.
They attract insects with the odor of nectar. Once inside, the insect finds it cannot get a grip on the walls of the pitcher because a flaky wax on the interior surface peels off as it struggles to climb. Eventually, it falls into the water and struggles to escape. The motion caused by the struggle stimulates digestive glands to release a digestive acid. This acid is so strong that a midge will disappear within hours. The largest of these, the Rajah pitcher, is able to digest mice! Like our own pitcher plant, this one too has its live inhabitants, the largest of which is a small crab.
is shrub-like carnivorous plant, normally growing to be 40-50 cm in height (maximum 150 cm). Stems are 5-15 mm thick and tend to creep along the ground as they become longer. Ten or more slender, needle-like, triangular shaped leaves are generally found per apical rosette. Leaves typically reach lengths of 10-25 cm with a width of 2.5 mm.
The master of sticky fly paper, Drosera (sundew), is a slow trap compared to the one in Venus Flytrap. However, the sundew relies on first trapping its prey with its sticky, glandular hairs, as shown in Figure 1, before it slowly rolls up the edges of the leaf. It does not fold like the Venus fly trap, but it can effective enclose small flies with the numerous hairs.
The sundews, so named because their glandular leaf hairs glisten like dew in the sun, are not only common in bogs, but can occur on sandy banks and other mineral soils poor in organic nitrogen and phosphorus. So fascinating is this tiny plant that Darwin (1875) spent 285 pages of his book on insectivorous plants describing his own experiments on it.
The hairs are stalked glands (Figure 3, 4 & 5) and produce digestive juices that decompose the trapped prey. These digestive enzymes, including protease and phosphatase, increase in production once a prey has been captured, reaching maximum concentration about the fourth day. Although one sundew is hardly an effective means of eliminating insect pests, Oliver (in Heslop-Harrison, 1978) counted insects trapped in a sampling of plants in England and estimated that about six million insects were trapped in a bog of about two acres!
Near the crease where the two leaf "jaws" join there is a series of tiny hairs. If an unwary insect walks across these hairs, touching two or more of them in succession, the leaf will close quickly enough to prevent its escape. Unable to escape between the hair-like teeth at the edge of the leaf (Figure 3), the helpless insect is slowly digested and absorbed by the leaf. Glands on the leaf surface secrete several digestive enzymes that help to decompose the insect. Once the insect has been digested sufficiently, the leaf re-opens for another victim.
The sensitive hairs at the fold of the leaf prevent the leaf from closing every time a drop of rain lands on it, because the leaf requires that two or more of these hairs be triggered in succession (Figure 3). If the leaf does close without a victim, it will re-open in a few hours. According to Lloyd (in George 1962), the traps can only catch about three victims before the leaves turn black and die. And even if the trap fails to catch anything, like when you tease it by touching a hair with a small brush, it can only reopen and close again about seven times!
So, don't tease the flytrap!
- the Albany Pitcher Plant
, the only known species in this genus, is native to the extreme southwestern part of Australia (near the town of Albany) where it lives on the margins of freshwater wetlands, ditches, and slow streams. It grows from underground rhizomes and its evergreen leaves hug the ground. It isn't related to other pitcher plants, although it has some features that resemble them. In this picture, you can see, at the center, the "ordinary" leaves, which are just flat, as well as some of the leaves which have the pitcher form and can catch insects. The plant produces two types of leaves. In the spring it produces a normal photosynthetic leaf that is not shaped like a trap. These last only one year and provide the plant with its stored carbon through photosynthesis. As these leaves reach their peak production, pitcher leaves begin to appear. Although these resemble those of Nepenthes, they are attached to their stalks at the back, whereas in Nepenthes they are attached at the base. And they are generally smaller, mostly about 3 cm (little over an inch), reaching a maximum of 6 cm, except in some cultivated varieties. Once the leaves mature, the lids open and expose the pitcher full of digestive fluid. Ribs on the outside of the pitchers are adorned with nectar glands that attract insects, mostly ants, and lure them to the open trap. The lids may close if the plant begins to dry, thus protecting it from loss of its digestive fluid.
• Clearing and degrading habitat for residential, agricultural, silvicultural, and industrial purposes.
• Hydrological changes resulting from dam and impoundment construction.
• Trampling and soil disturbance by cattle.
• Collection by plant enthusiasts, botanists, and commercial dealers.
• Fire suppression.
From the USFWS Recovery Plan 1994
When someone mentions endangered species, polar bears, tigers or sea turtles might come to mind. Not to degrade the importance of these species, but there is a tremendous list of other endangered species that are equally (or maybe even more) important to the biosphere.Take plants, for example. Have you ever cared that a plant other than a big beautiful tree was in danger of extinction? Did you even know that plants were on the endangered species list? There are so many plant species out there, and they are all pretty much the same -- green leaves, flowers, roots -- that it won't matter if a few of them disappear. There will be another closely related species that will be able to fill the extinct plant's niche, right? No way!Plants, like all organisms in an ecosystem, occupy a specific niche. A niche is the ecological role an organism plays in its community, i.e. what it eats, where it lives, what eats it, what nutrients it supplies to the system and so forth. Many niches overlap, but through the process of evolution, organisms have evolved to play different, yet important roles in their communities.
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