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The Venus flytrap (also referred to as Venus's flytrap or Venus' flytrap), ''Dionaea muscipula'', is a carnivorous plant native to subtropical wetlands on the East Coast of the United States in North Carolina and South Carolina.〔(Kew World Checklist of Selected Plant Families )〕 It catches its prey—chiefly insects and arachnids— with a trapping structure formed by the terminal portion of each of the plant's leaves and is triggered by tiny hairs on their inner surfaces. When an insect or spider crawling along the leaves contacts a hair, the trap closes if a different hair is contacted within twenty seconds of the first strike. The requirement of redundant triggering in this mechanism serves as a safeguard against a waste of energy in trapping objects with no nutritional value. ''Dionaea'' is a monotypic genus closely related to the waterwheel plant and sundews, all of which belong to the family Droseraceae. ==Description== 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;〔(【引用サイトリンク】 work = The Carnivorous Plant FAQ )〕 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. (These protrusions, and the trigger hairs, also known as sensitive hairs, are probably homologous with the tentacles found in this plant’s close relatives, the sundews.) Scientists have concluded that the Venus flytrap is closely related to ''Drosera'' (sundews), 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''. The Venus flytrap exhibits variations in petiole shape and length and whether the leaf lies flat on the ground or extends up at an angle of about 40–60 degrees. The four major forms are: 'typica', the most common, with broad decumbent petioles; 'erecta', with leaves at a 45-degree angle; 'linearis', with narrow petioles and leaves at 45 degrees; and 'filiformis', with extremely narrow or linear petioles. Except for 'filiformis', all of these can be stages in leaf production of any plant depending on season (decumbent in summer versus short versus semi-erect in spring), length of photoperiod (long petioles in spring versus short in summer), and intensity of light (wide petioles in low light intensity versus narrow in brighter light). When grown from seed, plants take around four to five years to reach maturity and will live for 20 to 30 years if cultivated in the right conditions. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Venus flytrap」の詳細全文を読む スポンサード リンク
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