1.  Venus Flytrap   GENUS Dionaea               

General

Probably the best known among all carnivorous plants because of its swift movement of trap leaves, the Venus flytrap (Dionaea muscipula) grows in the coastal savannas of North and South Carolina in the United States. This is the only region in the world where the plants can be seen in their native habitat. The plants are typically found on a moist surface in the open pine tree forest, sometimes on a thick mat of sphagnum moss, sometimes right on the white sand surface, often in company of other carnivorous plants in the area such as sundews and terrestrial bladderworts.

The plants are federally protected ..????..

The genus name Dionaea is from Dione, the goddess of love, in Greek mythology. Venus, in Roman religion, is identified with the Greek goddess, Aphrodite, whose mother, according to one account, is Dione.

The genus Dionaea is monotypic; that is, there is only one species, Dionaea muscipula. The genus belongs to the sundew family Droseraceae.

Historical Note

 In a historical letter dated Jan. 24, 1760, Arthur Dobbs, then Governor of North Carolina, wrote, " ...But the great wonder of the vegetable kingdom is a very curious unknown species of sensitive; it is a dwarf plant; the leaves are like a narrow segment of a sphere, consisting of two parts, like the cap of a spring purse, the concave part outward, each of which falls back with indented edges (like an iron spring fox trap); upon anything touching the leaves, or falling between them, they instantly close like a spring trap, and confine any insect or anything that falls between them; it bears a white flower; to this surprising plant I have given the name of Fly Trap Sensitive."

Description

The Venus flytrap uses a snap trap (sometimes referred to as steel trap), the most advanced trap mechanism to be found among carnivorous plants. The plant forms a rosette of leaves emerging from a short white rhizome (underground stem) with fibrous roots. The leaves, which can grow up to 10cm, are of two parts: a flat petiole (leaf stem) and a leaf blade modified into a trap.

The trap portion consists of two semicircular lobes united along the midrib of the leaf blade. Around the margin of each lobe grow stiff, spine-like guard hairs (15 to 20 along each margin), which mesh together when the trap closes to prevent the prey's escape. Along the inner edge of each lobe just below these marginal spines runs a narrow band of nectar glands which secrete sugary substance to attract potential prey. Much of the inner lobe below is crowded with numerous digestive glands, which often give the trap surface a bright-red coloration. Each inner lobe surface has three -- sometimes 4 or more -- fine bristles located in a triangular pattern. These are trigger hairs, which are sensitive to physical stimulation and, when properly stimulated, initiate a rapid trap closure.

Prey Capture

When an unwary insect brushes these hairs, the trap snaps shut, usually in less than half a second. The guard hairs of each lobe mesh together to prevent the insect's escape, and the prey is hopelessly confined between the two lobes. The insect's effort to free itself further irritates the trigger hairs, causing the lobes to close more tightly. This pressure sometimes crushes a soft-bodied insect. In several hours, as the lobes are tightly sealed, the trap becomes filled with digestive fluids secreted from the glands on the lobe surface, and the captured prey begins to dissolve. The trap remains closed during the digestive process which lasts for a week to ten days depending on the size of the prey. After the nutrients of the insect body are absorbed by the plant, the trap opens slowly. Inside the now dry trap is the remains of the hard shell part of the consumed insect. Wind and rain clean the lobes and the trap is ready again for another meal. A single trap is usually capable of repeating this process only three times or so during the life of the trap. After that it becomes insensitive to stimulation and dies, but new trap leaves are continuously sprouting out from the rosette center during the growing season of spring through summer.

When a trigger hair is stimulated by a piece of wood, or a finger, the trap also snaps shut. In this case, however, the trap opens the next day, since the plant does not find any nutritious object inside the trap.

Screening of Prey

Typically, insects and other small bugs -- such as flies, ants, and spiders -- are known to be prey for the plants in the wild. When the plant is in a vigorous growing condition, one often observes a band of wet surface along the margin of the blades. This is due to secretions from the nectar glands. Apparently, a sweet nectar is an important factor to allure prey, along with visual attraction of the bright coloration of the trap interior. Indeed, anyone who has ever observed an insect licking the nectar, as I have, will be convinced that there is something almost intoxicating in the exudation from the nectar glands.

With its mouth working on the inner margin of the lobe where nectar is being served, an insect large enough in size to brush against some of the trigger hairs ends up tripping the deadly trap. The trigger hairs are so situated, in relation to the nectar band, that, given a mature trap of 20-30mm in length, an insect less than 5mm or less is not likely to trigger the trap. Considering the amount of energy needed for a tiny plant to close the trap, this preliminary screening of prey large enough to make it worth the effort can be construed as an economic measure of a sort. Lloyd cites a report showing that, of fifty closed traps examined, only one contained the catch less than 5mm in length, and only seven less than 6mm in length. All the other catches were 10-30mm in length.

There are two phases in the trap closure. The initial phase is characterized by a quite rapid movement of the trap lobes that brings guard hairs on the edge of both lobes together, close enough to interlace them. This will effectively entrap the prey of sufficient size inside the trap, while leaving some open spaces between interlaced guard hairs for small er prey to escape -- the second screening of prey, if you will -- before proceeding to the digestive phase.

Multiple Stimulation Requirement

It is well known among growers that, in order to close the trap, not one but two stimulations are required: either two different trigger hairs must be each stimulated once, or a single trigger hair stimulated twice. This is the plant's clever way of making sure that the prey about to be snapped has reached the center of the trap before triggering the trap. This delay strategy increases the chance of a successful catch. With each snap consuming so much energy, the Venus flytrap can not afford too many misses. It is also observed that a mild rain usually does not trigger the trap.

Many experiments have been conducted on this snap trap behavior of the plant. In a normal condition, stimulating a trigger hair once does not cause a trap movement. To initiate a successful closure, it is necessary to stimulate two different hairs, or stimulate the same hair twice, within a 20 seconds or so interval. If the two stimuli are given in a rapid succession, a quite swift closure -- well under half a second -- immediately follows. The longer the interval between two stimuli, the less rapid the closure becomes. If it is within 20 seconds, a rapid trap closure usually occurs within a few seconds. If the second stimulus takes place after a half minute or later, however, the closure itself becomes extremely slow and multiple stimuli may be required to complete the closure. On the other hand, in the height of a growing season, if the temperature is 35 degrees C or higher, a trap closure may occur by one stimulus only. It is also noted that the stimulation to the lobe part, other than the trigger hairs themselves, particularly the area near the hairs, does sometimes induce trap closure.

Studies have shown that sensory cells responsible for triggering the trap are located near the base of the trigger hair, at the indentation where bending strains are most pronounced when hairs are touched. Action potentials have been observed upon bending of the trigger hairs.

Closure Mechanism

A sudden drop of the cellular pressure on the inner surface of the lobes causes the imbalance to the higher pressure of cells on the outer surface, thus precipitating a sudden closing action of the trap. The reopening phase, on the other hand, proceeds rather slowly, taking several hours. Unlike the rapid closing phase, it is due to cell growth. A growth rate of an activated leaf is higher than an undisturbed trap and a reopened lobe has been measured to be several percent larger than the original size.

The trap can be made to close by mechanical stimulation to the trigger hairs. The trap reopens the next day if the trap is empty, or only contains inanimate object with no nutritious value to the plant. Each trap can be "fooled" to close several times before it reaches its growth maturity and ceases to function.

Digestion and Absorption

The initial phase of rapid closure is followed by what is termed the narrowing phase. This second phase is pursued only if the trap catches something nutritious to the plant, or if the stimulus is continuously coming as would be the case if a live insect is captured. The narrowing phase is a slower process which brings the margin of two lobes tightly together. Often the pressure exerted in this phase is strong enough to crush a soft-bodied insect prey, thus possibly causing chemical stimulation.

As the lobes are tightly sealed, digestive fluids are secreted from the digestive glands into the closed trap interior. The prey, if still alive, will most probably be suffocated in the fluids. The digestive secretions which is known to be initiated only by proper chemical stimulation typically begins a day or so after the capture of prey, although such protein-rich substances as egg-whites may often induce copious secretions in a matter of a few hours. Digested material is then absorbed through the glands and through the inner surface of the trap.

The digestive process, not unlike that of an animal's stomach, lasts for a few days to a week, depending on the size of the prey. When the digestion/absorption process is over, the trap (now dry) reopens, revealing the chitinous remains of the prey. The wind and rain clean the lobes, and the trap is ready again for another meal. Each trap is capable of completing the whole digestive process two or three times at most before it ceases to function. Too large a catch often results in the damage of the trap, as the trapped animal begins to decay, causing the entire leaf blade to blacken and die out before the digestion is complete -- an upset stomach, as it were.

Inflorescence                           

In the early spring, a flower bud appears in the rosette center. In a month or so, this develops into a tall scape (flower stem) bearing many white flowers. A scape often reaches a height of 20-30cm in nature, providing a possible spatial separation of pollinators and prey. An actinomorphic flower (radially symmetric) with five petals bloom in May through June in North Carolina. An elegant, white flower is shot with green veins on the petal. Each flower typically opens for 2-3 days. Numerous black seeds fully mature by late July. As the seed capsule dries, the pressure from capsule shrinkage bursts the slippery, pear-shaped seeds around the field.

In nature, the seeds germinate shortly after the dispersal and tiny seedlings have a few months to prepare for the onset of winter. In spite of A relatively small size of the plant, It takes 3 to 4 years for the seedling of the Venus flytrap to reach a flowering age. The plant is said to live for 20-25 years.

Birth of flytraps. Two-day^
old. Germination begins as
jet-black, pear-shaped
seeds take up water and
swell. The embryonic root
then emerges from the seed
coat, from which sprout
root hairs.

Two-week old seedlings, 5 tnr" tall. As the root hairs anchor in the earth,
twin cotyledons --- seed leaves --- appear. These cotyledons have no traps
on them, but the leaf right after the cotyledons does have a miniature trap.
The Venus' flytrap matures from seedling to flowering age in 3"1* years.

In May through June, many white flowers bloom at the tip of a tall flower stem rising from the center of the plant. Seeds mature by mid-summer, and tiny Venus flytrap babies are produced. It takes 3-4 years for the seedlings to reach flowering age.

This build-up of a threshold potential before a trap motion is actually triggered is considered advantageous for the Venus flytrap. This ensures a successful catch in many cases, by properly positioning the prey in the center of the trap plate before a trapping attempt, rather than closing the trap prematurely when much of the insect's body may still be outside the trap.

Introduction  VenusFlytrap  Sundews  PitcherPlants  CobraPlant  Butterworts  Bladderworts