The Venus Flytrap
The Form and Growth of Dionaea muscipula
The Venus Flytrap has a fascinating, complex leaf trap and amazing ability to move quickly to capture prey. But relative to many other plants, the Venus Flytrap is a rather simple, primitive plant in structure. Many plants have a central stalk (or trunk), often subdivided, from which leaves grow, with a well defined and usually branched root system attached to this or another type of intermediate tissue structure between the roots and leaves. But Venus Flytraps have no stalk, no intermediate tissue between roots and leaves. In fact, Venus Flytraps are composed only of leaves, and rather than sharing a root system, each leaf grows its own root or roots, and each root is a single structure, not dividing or branched. It could be said that every mature leaf of a Venus Flytrap is an entire plant capable of being autonomous (self-sustaining). Each new leaf shares some tissue with the group of older leaves from which it grows, but when it forms its own roots, the leaf could be removed from the rest of the clump, potted and considered a separate plant, and a single Venus Flytrap could be regarded, from one point of view, as a collection of individual plants.
Because healthy Venus Flytraps can more or less continuously produce new leaves to replace old ones that die, a single Venus Flytrap can live for as long as conditions allow, and Venus Flytraps can easily outlive the humans who cultivate and care for them. There is a Venus Flytrap clone called 1955 that began life as a Venus Flytrap that carnivorous-plant grower and expert Bob Ziemer bought in the year 1955. This Venus Flytrap has lived continuously since then not only in Bob Ziemer's care but also grown by the recipients of many divisions (small offshoot plants) produced by the 1955 Venus Flytrap.
General Growth Habit
After a Venus Flytrap seed germinates, the seedling will grow at the soil's surface, with a thin, short root and two (sometimes three) tiny trapless seed leaves (the cotyledons). Then as the first few trap-bearing leaves grow, they begin to bury themselves by growing a little downward into the soil before growing upward from the soil's surface into the light. They use the light (in the process of photosynthesis) to create food for themselves that they then store at the base of the leaf, underground.
As successive new leaves grow, they become larger and bury themselves deeper into the ground, until there is a group of leaves the bases of which are all under the surface. These leaf bases swell with stored food. During the summer, the active growing season, much of the food created by photosynthesis is used by the plant to produce new leaves. During the Fall and Winter, when growth slows and the plant becomes dormant, it continues to photosynthesize and store food in the base of the leaves, to provide the nutrients necessary for vigorous growth in the Spring when the plant emerges from dormancy. In this sense the Venus Flytrap is never truly dormant. It grows only slowly during the cool-to-cold weather months, but it nevertheless grows a little, and it continues to need light and to produce food for itself from that light, whether the traps, sluggish during cold weather and dormancy, are able to catch any prey at that time or not.
Because each leaf can and usually does produce its own root(s), entire Venus Flytrap plants can be grown from a single leaf pulled from a Venus Flytrap. These "leaf cuttings" (or "leaf pullings") are one method to propagate Venus Flytraps that are genetically identical to each other, unlike Venus Flytraps grown from seed.
Although a Venus Flytrap appears to grow in a rosette, with leaves growing from the center and radiating outward in all directions. The leaves actually tend to grow from one side of the "rhizome" (the "bulb" or more accurately the group of leaf bases underground), and over the course of a year the entire plant and the center of its rosette can move an inch or more (several centimeters) in some particular direction.
Seasonal Growth Habit
Venus Flytrap leaves grow differently in cool weather and in warm weather. When the air is often cool to cold in the late Fall, Winter and early Spring, Venus Flytrap leaves grow short and stay very close to the surface of the soil. This helps to keep them warm by means of the heat radiating from the gigantic thermal mass of the soil surrounding them, which cools much more slowly than the air above the surface. Even when the air is freezing, the temperature at ground level is often above freezing and the leaves of Venus Flytraps can continue to live and photosynthesize.
If the air is too cold (below freezing) for too long, the part of the Venus Flytrap leaf that is above ground might freeze and die, but the base of the leaves underground rarely freeze in the Venus Flytrap's natural environment, and new leaves emerge from the leaf bases when the weather warms a little.
During the active growing season from late Spring through mid-Fall, the leaves of most Venus Flytraps grow more upright and are often thinner than the short and prostrate (ground-hugging) growth of cold weather and dormancy. This more upright growth helps to expose the leaves to a greater amount of light (as mentioned elsewhere at VenusFlytrap.info, Venus Flytraps love light) and perhaps makes the traps more attractive as landing perches for insects, some of which it captures.
Flowering and Seeding
Once per year in Spring Venus Flytraps produce a flowerstalk (sometimes two or more) from the center of the plant which grows usually from 8 inches to over 24 inches in height (20-60 centimeters). Like many annual or biennial plants, a Venus Flytrap rosette (a circle of leaves radiating from a single central point) will flower and produce seed as a last act before it dies. In the case of the Venus Flytrap however, even though a particular growing crown or rosette of leaves dies, a plant in good health continues to survive by producing fresh, new growing crowns, new divisions, from the stored food in the rhizome underground. The leaves of the rosette that produces a flowerstalk may continue to live for weeks or up to several months after the plant flowers, but will slowly brown and die even as the new plantlets (divisions) begin to grow from the rhizome and emerge above the soil surface, and no new leaves will be produced by the older, already-flowered rosette.
Venus Flytrap flowers when pollinated by insects each produce from several to a couple dozen tiny, shiny black seeds. Unlike plants that bloom in the Fall and produce seed adapted to wait until the cold weather of Winter has ended before germinating, Venus Flytrap seeds fall to the ground in the Summer and usually germinate and begin to grow within 10 to 25 days. For more information about the flowering and seed production of Venus Flytraps, see the article "Grow Venus Flytraps from Seed" here at VenusFlytrap.info.
Young, weak or sickly plants, or those that have recently been transplanted, should not be allowed to flower because the flowering and seed-producing process uses up much of the stored food in the Venus Flytrap's rhizome. Such plants can become further weakened or even die as a result, so the emerging flower stalks should be cut from such weak or sick plants shortly after the flowerstalks appear in mid to late Spring. Only mature, healthy Venus Flytraps should be allowed to flower and set seed.
Venus Flytrap Trapping Mechanism
The leaves of a Venus Flytrap have thin, often wide flanges to either side of the petiole (the leaf stem) to create a large surface exposed to sunlight in order to produce food inside the leaves in the process of photosynthesis. At the end of the petiole is the true leaf, which is also the amazingly structured trap of the Venus Flytrap. This trap often turns deep red and produces a sweet nectar around its edges which entices flies and other insects (and sometimes spiders, small frogs or lizards) into the traps.
The structure of the inside of the Venus Flytrap's trap, showing the trigger hairs
The traps are edged with sharp spines which, when the trap closes, look like interlaced fingers on a human hand and act like bars on a prison cell, confining a trapped insect inside. Protruding from the inside surface of each trap are several short "trigger hairs" that are extremely sensitive to movement. When they are touched or even slightly moved, they produce a chemical reaction inside the leaf (the trap). If a trigger hair is touched or moved twice within 30 seconds or so, or if two different trigger hairs are touched, the trap will usually close, often very quickly. Even a slow-moving trap will often capture an insect that is more focused on the nectar it is sipping than the slow movement of the leaf that is closing around it.
Closeup of the sensitive trigger hairs and the tiny red digestive glands inside the trap of a Venus Flytrap
Once an insect is captured, it continues to touch and move the trigger hairs inside the trap, which begins another process. The leaf begins to slowly close tight, until it forms a seal around all the edges of the trap. Then the many tiny digestive glands covering the inside surface of the trap begin to exude a fluid containing digestive enzymes that first kills the insect (by flooding the inside of the trap and drowning the insect) and then digests all the softer parts of the insect over the course of about 5 to 10 days, after which the trap absorbs the fluid with all the nutrients it has gained from the insect and then opens again, leaving only the hard, chitinous exoskeleton of the insect, which either remains in the trap (it doesn't prevent the trap from capturing more prey) or is washed out by rain or blown out by wind.