Venus flytrap

Appearance

The Venus flytrap is a small plant whose structure can be described as a rosette of four to seven leaves, which arise from a short subterranean stem that is actually a bulb-like object. Each stem reaches a maximum size of about three to ten centimeters, depending on the time of year; longer leaves with robust traps are usually formed after flowering. Flytraps that have more than 7 leaves are colonies formed by rosettes that have divided beneath the ground.

The leaf blade is divided into two regions: a flat, heart-shaped photosynthesis-capable petiole, and a pair of terminal lobes hinged at the midrib, forming the trap which is the true leaf. The upper surface of these lobes contains red anthocyanin pigments and its edges secrete mucilage. The lobes exhibit rapid plant movements, snapping shut when stimulated by prey. The trapping mechanism is tripped when prey contacts one of the three hair-like trichomes that are found on the upper surface of each of the lobes.

The trapping mechanism is so specialized that it can distinguish between living prey and non-prey stimuli such as falling raindrops; two trigger hairs must be touched in succession within 20 seconds of each other or one hair touched twice in rapid succession, whereupon the lobes of the trap will snap shut in about one-tenth of a second. The edges of the lobes are fringed by stiff hair-like protrusions or cilia, which mesh together and prevent large prey from escaping. Scientists have concluded that the Venus flytrap is closely related to ''Drosera'' , and that the snap trap evolved from a fly-paper trap similar to that of ''Drosera''.

The holes in the meshwork allow small prey to escape, presumably because the benefit that would be obtained from them would be less than the cost of digesting them. If the prey is too small and escapes, the trap will reopen within 12 hours. If the prey moves around in the trap, it tightens and digestion begins more quickly.

Speed of closing can vary depending on the amount of humidity, light, size of prey, and general growing conditions. The speed with which traps close can be used as an indicator of a plant's general health. Venus flytraps are not as humidity-dependent as are some other carnivorous plants, such as ''Nepenthes'', ''Cephalotus'', most ''Heliamphora'', and some ''Drosera''.

Naming

The plant's common name refers to Venus, the Roman goddess of love. The genus name, ''Dionaea'', refers to the Greek goddess Aphrodite, while the species name, ''muscipula'' is Latin for "mousetrap".

Historically, the plant was also known by the slang term "tipitiwitchet" or "tippity twitchet", possibly an oblique reference to the plant's resemblance to human female genitalia.

Status

Currently, there are estimated to be more than 3–6 million plants in cultivation compared to only 35,800 plants remaining in nature. Several prominent plant conservationists suggest that the plant be labeled as Vulnerable. Precise data on the distribution of population sizes in 1992 from the Office of Plant Protection suggests a more dire state for the species. Every size class in red is slated for eventual extinction with the green ones persisting longer. Smaller populations may go extinct for stochastic reasons and, since small population are more numerous in nature now and contribute more to the total number of plants remaining in the species, most of this unique and remarkable carnivorous plant species may be going extinct soon. Note that the figure of 35,800 plants in 1992 is over 20 years old and may not accurately reflect the current situation.

Habitat

The Venus flytrap is found in nitrogen- and phosphorus-poor environments, such as bogs and wet savannahs. Small in stature and slow growing, the Venus flytrap tolerates fire well, and depends on periodic burning to suppress its competition. Fire suppression threatens its future in the wild. It survives in wet sandy and peaty soils. Although it has been successfully transplanted and grown in many locales around the world, it is found natively only in North and South Carolina in the United States, specifically within a 60-mile radius of Wilmington, North Carolina. One such place is North Carolina's Green Swamp. There also appears to be a naturalized population of Venus flytraps in northern Florida as well as an introduced population in western Washington. The nutritional poverty of the soil is the reason that the plant relies on such elaborate traps: insect prey provide the nitrogen for protein formation that the soil cannot. The Venus flytrap is not a tropical plant and can tolerate mild winters. In fact, Venus flytraps that do not go through a period of winter dormancy will weaken and die after a period of time.

Evolution

The carnivorous diet is a very specialized form of foliar feeding, and is an adaptation found in several plants from soil poor in nutrients. Their carnivorous traps were evolutionarily selected to allow these organisms to survive their harsh environments.

The "snap trap" mechanism so characteristic of ''Dionaea'' is shared with only one carnivorous plant genus, ''Aldrovanda''. This relationship was thought to be coincidental, more precisely convergent evolution, for most of the 20th century - some phylogenetic studies even suggested that the closest living relative of ''Aldrovanda'' was the sundew. It was not until 2002 that a molecular evolutionary study indicated that ''Dionaea'' and ''Aldrovanda'' did in fact share a most recent common ancestor by analysis of combined nuclear and chloroplast DNA sequences.

A 2009 study presented evidence for the evolution of snap traps of ''Dionaea'' and ''Aldrovanda'' from a flypaper trap like ''Drosera regia'', based on molecular data. The molecular and physiological data implies that ''Dionaea'' and ''Aldrovanda'' snap traps evolved from the flypaper traps of a common ancestor with the ''Drosera''. Pre-adaptations to evolution into snap-traps were identified in several species of ''Drosera'', such as rapid leaf and tentacle movement. The model proposes that plant carnivory by snap-trap evolved from the flypaper traps driven by increasing prey size. Bigger prey provides higher nutritional value, but large insects can easily escape the sticky mucilage of flypaper traps; the evolution of snap-traps would prevent escape and kleptoparasitism , and would also permit a more complete digestion.Carnivorous plants are generally herbs, and their traps primary growth. They generally do not form readily fossilizable structures such as thick bark or wood. As such, there's no fossil evidence of the steps that would link ''Dionaea'' and ''Aldrovanda'', or with their common ancestor with ''Drosera''. Despite that, it's possible to extrapolate an evolutionary history based on phylogenetic studies of both genera. So, the researchers proposed a series of steps that would ultimately result in the complex snap-trap mechanism:

⤷  Larger insects usually walk over the plant, instead of flying to it, and are more likely to break free from sticky glands alone. Therefore, a plant with wider leaves, like ''Drosera falconeri'', must have adapted to move the trap and its stalks in directions that maximized its chance of capturing and retaining such prey - in this particular case, longitudinally. Once adequately "wrapped", escape would be more difficult.
⤷  Then, evolutionary pressure selected the plants with shorter response time, in a manner similar to ''Drosera burmannii'' or ''Drosera glanduligera''. The faster the closing, less reliant on the flypaper model the plant would be.
⤷  As the trap became more and more active, the energy demanded to "wrap" the prey increased. Therefore, plants that could somehow differentiate between actual insects and random detritus/rain droplets would be in advantage, thus explaining the specialization of inner tentacles into trigger hairs.
⤷  Ultimately, as the plant relied more in closing around the insect rather than gluing them, the tentacles so evident in ''Drosera'' would lose its original function altogether, becoming the "teeth" and trigger hairs — an example of natural selection hijacking pre-existing structures for new functions.
⤷  Completing the transition, at some point in its evolutionary history the plant developed the depressed digestive glands found inside the trap, rather than using the dews in the stalks, further differentiating it from the ''Drosera'' genus.