Carnivorous Plants Essay, Research Paper

Carnivorous Plants

In a world where plants are at the bottom of the food-chain, some

individual plant species have evolved ways to reverse the order we expect to

find in nature. These insectivorous plants, as they are sometimes called, are

the predators , rather than the passive prey. Adaptions such as odiferous lures

and trapping mechanisms have made it possible for these photosynthesizers to

capture, chemically break-down and digest insect prey (and in some cases even

small animals.) There is no reason to fear them though. The majority are

herbaceous perennials, usually only 4 to 6 inches high, and nothing like the

plant in “Little Shop of Horrors”.

Almost all carnivorous plants have a basically similar ecology and

several different species are often found growing almost side by side. They are

most likely to be found in swamps, bogs, damp heaths and muddy or sandy shores.

Drosophyllum lusitanicum from Portugal and Morocco is the one exception, it

grows on dry gravelly hills. Like other green plants, carnivorous plants

contain the organic pigment chlorophyll. This pigment helps to mediate a

chemical process called photosynthesis. This converts light energy into the

chemical bond energy of carbohydrate which is utilized as cellular energy, plant

growth and development. Water, carbon dioxide, nutrients and minerals are also

needed for survival. In wetlands, where stagnate water contains acidic

compounds and chemicals from decaying organic matter many plants have a

difficult time obtaining necessary nutrients. It is in these nutrient poor

conditions that some plants evolved different ways of obtaining nutrients. The

ability of carnivorous plants to digest nitrogen -rich animal protein enables

these plants to survive in somewhat hostile environments.

The evolution of carnivorous plants is speculative due to the paucity of

the fossil record. It is believed that plant carnivory may have evolved millions

of years ago from plants whose leaves formed depressions that retained rain

water. Small insects would sometimes fall into these water reservoirs and drown,

eventually being decomposed by bacteria in the water. The nutrients from the

insects would be absorbed by the leaf. The deeper the leaf depression the more

insects that could be drowned. This would have created a distinct survival

advantage allowing some plants to better compete in nutrient poor soil. As time

passed, these plants would evolve more effective trapping mechanisms.

There are more than 500 known species of carnivorous plant, although

some are now extinct. Classification is done using the standard binomal system

and is based primarily on the floral characteristics of the plants, not the

trapping mechanisms. They are divided into two groups based on corolla

structure; Choripetalae and Sympetalae. The group of plants categorized as

carnivorous belong to seven families, which are recognized by the suffix ?aceae’,

and fifteen genera. More than half of the species belong to the family

Lentibulariacene that is marked by bilaterally symmetrical flowers with fused

petals. The remainder of the species belong to six families marked by radially

symmetrical flowers with separate petals. Classification is illustrated in the

chart below in addition to the geographic range, the number of species, and the

type of trapping mechanism.

Family Genus species Geographic

Distribution Type of Trap Byblidaceae Byblis

2 Australia Passive flypaper

Cephalotaceae Cephalotus 1 S.W.

Australia Passive pitfall Dioncophyllaceae

Triphyophyllum1 West Africa Passive flypaper

Droseraceae Aldrovanda 1 Europe, Asia,

Africa, Australia Active

Dionaea1 North & South Carolina

Active steel Family Genus # of species

Geographic Distribution Type of Trap

Drosera 120 Omnipresent Passive

flypaper

Drosophyllum1 Morocco, Portugal, Spain

Passive flypaper NepenthaceaeNepenthes 71

East Indies Passive pitfall Sarraceniaceae

Darlingtonia1 California & Oregon, Passive

pitfall

Western Canada

Heliamphora6 North and South

America Passive pitfall

Sarracenia9 North America

Passive pitfall LentibulariaceaeGenlisea 14

Tropical Africa and Passive lobster

South America,

Madagascar

Pinguicula 50 Northern

Hemisphere and Passive pitfall

South America

Polypompholyx2 Australia

Active mousetrap

Ultricularia 300 Omnipresent

Active mousetrap

In the above chart, it can be seen that there is a large number of

different types of traps. The modified leaf traps of carnivorous plant can each

can be categorized as either active or passive. An active trap is one that

employs rapid movement as an integral part of the trapping mechanism, a passive

trap does not use rapid movement.

Active traps are categorized as “steel” or “mousetrap”. Active steel

type traps consists usually of two rectangular lobes that are hinged on one side.

The two lobes move rapidly toward each other to entrap prey when stimulated.

Active mousetraps are suction traps that use egg-shaped leaves or bladders that

have an opening with a door on one side. When trigger hairs on the door are

touched the leaf releases pressure and sucks the prey into the trap. In the

aquatic species of the genus Utricularia, this is the most complex and rapidly

acting trap; prey is sucked up into the bladders in 1/30 of a second.

There are three types of passive traps; “pitfall traps”, “lobster traps”,

and “flypaper traps”. Not completely passive, Lobster traps employ slow moving

tentacles that are powered by cell growth. These plants lead prey into their

trap using these two hairy spiral arms to guide the prey. Many plants capture

prey by forming clever containers creatures enter but can not escape from.

Passive pitfall traps, such as the ones employed by the butterworts (genus

Pinguicula) and pitcher plants (Darlingtonia, Sarraceniaceae, & Nepenthes),

attempt to lure insects into their cylindrically shaped hollow vessel and into

it’s stomach, which is often referred to as the pitcher. The insects get stuck

in the digestive enzymes of the pitcher and die. Flypaper traps, such as the

sundew (Drosophyllum & Drosera), produce sticky mucilage that covers the upper

surface of its leaves. Insects become mired in this and leaves then bend around

or roll up to enclose the prey for digestion.

Within the carnivorous plant world there are some truly amazing plants.

Of all the hundreds of species Dionaea muscipula, the Venus fly trap, is

probably the most dramatic. It is the only species in it’s genus and there are

no other plants quite like it. It’s hinged leaf lobes are capable of snapping

shut on prey in less than a half a second, eventually crushing the insect. Like

many carnivorous plants, the Venus fly trap lures prey in with bate, which in

this case is the smell of nectar. When an insect enters one of the bizarre

traps it might bend one of the three stiff trigger hairs in the center of the

leaf. When bent a couple of times in succession these hairs activate the trap.

The plant does not have muscle tissue, the process of closing instead involves

electrical signals and changes in water pressure. The book The Nature of Life

briefly describes the process of the Venus fly trap closing once triggered by

saying that:

trigger cells at the foot of the hair are deformed, as if pried

by a lever. Stimulated by the stress, trigger cells generate an

electric signal that flows from cell to cell through the leaf.

Specialized motor cells receive the signal, change shape, and cause

the trap to close.

About ten days are needed for digestion after which the leaf slowly opens up

again revealing only the undigestible chitin remains. The trap, not the plant

itself, turns black and dies when the plant tries to digest fats or eventually

after three or four captures.

The largest carnivorous plants belong to the genus Nepenthes. The vines

of these plants are usually tens of meters long. This genus is also capable of

catching some of the largest prey in their pitchers, including creatures as

large as frogs and small rodents. Nepenthes are unique amongst carnivorous

plants as the only dioecious genus, which means there are separate male and

female plants. These plants are very endangered and several species or extinct.

Some species of Nepenthes are sold for hundreds of dollars to collectors and are

involved in illegal overseas trade.

The growing of carnivorous plants has become very popular in recent

years. Unfortunately the endangered status of many species does not stop

collectors from risking high fines and field collecting them. This has had

seriously impact on many species, but collectors are not the biggest problem

facing carnivorous plants. In the USA and other developed countries wetlands

are considered useless and are being drained and developed on. At present it is

estimated that only 3-5% of carnivorous plant habitat remain in the US. Another

problem is that fires are put out before they spread even though many plants,

such as the Venus fly trap, benefit from periodic burns. Habitat destruction

from slash and burn agriculture, however, does not benefit any of the

carnivorous plants and is also causing a great deal of the extinctions.