page_title: Drosera
section_title: Leaves and carnivory
hierarchical_section_title: Drosera / Description / Leaves and carnivory
caption_attribution_description: Non-carnivorous emergences Drosera indica
context_page_description: Drosera, commonly known as the sundews, is one of the largest genera of carnivorous plants, with at least 194 species. These members of the family Droseraceae lure, capture, and digest insects using stalked mucilaginous glands covering their leaf surfaces. The insects are used to supplement the poor mineral nutrition of the soil in which the plants grow. Various species, which vary greatly in size and form, are native to every continent except Antarctica.
  Charles Darwin performed much of the early research into Drosera, engaging in a long series of experiments with Drosera rotundifolia which were the first to confirm carnivory in plants. In an 1860 letter, Darwin wrote, “…at the present moment, I care more about Drosera than the origin of all the species in the world.”
  Both the botanical name and the English common name refer to the glistening drops of mucilage at the tip of the glandular trichomes that resemble drops of morning dew. The Principia Botanica, published in 1787, states “Sun-dew derives its name from small drops of a liquor-like dew, hanging on its fringed leaves, and continuing in the hottest part of the day, exposed to the sun.”
context_section_description: Sundews are characterised by the glandular tentacles, topped with sticky secretions, that cover their laminae. The trapping and digestion mechanism usually employs two types of glands: stalked glands that secrete sweet mucilage to attract and ensnare insects and enzymes to digest them, and sessile glands that absorb the resulting nutrient soup (the latter glands are missing in some species, such as D. erythrorhiza). Small prey, mainly consisting of insects, are attracted by the sweet secretions of the peduncular glands. Upon touching these, the prey become entrapped by sticky mucilage which prevents their progress or escape. Eventually, the prey either succumb to death through exhaustion or through asphyxiation as the mucilage envelops them and clogs their spiracles. Death usually occurs within 15 minutes. The plant meanwhile secretes esterase, peroxidase, phosphatase and protease enzymes. These enzymes dissolve the insect and free the nutrients contained within it. This nutrient mixture is then absorbed through the leaf surfaces to be used by the rest of the plant.
  
                                                                                       
  All species of sundew are able to move their tentacles in response to contact with edible prey. The tentacles are extremely sensitive and will bend toward the center of the leaf to bring the insect into contact with as many stalked glands as possible. According to Charles Darwin, the contact of the legs of a small gnat with a single tentacle is enough to induce this response. This response to touch is known as thigmonasty, and is quite rapid in some species. The outer tentacles (recently coined as "snap-tentacles") of D. burmannii and D. sessilifolia can bend inwards toward prey in a matter of seconds after contact, while D. glanduligera is known to bend these tentacles in toward prey in tenths of a second. In addition to tentacle movement, some species are able to bend their laminae to various degrees to maximize contact with the prey. Of these, D. capensis exhibits what is probably the most dramatic movement, curling its leaf completely around prey in 30 minutes. Some species, such as D. filiformis, are unable to bend their leaves in response to prey.
  A further type of (mostly strong red and yellow) emergence has recently been discovered in a few Australian species (D. hartmeyerorum, D. indica). Their function is not known yet, although they may help in attracting prey.
  The leaf morphology of the species within the genus is extremely varied, ranging from the sessile ovate leaves of D. erythrorhiza to the bipinnately divided acicular leaves of D. binata.
  While the exact physiological mechanism of the sundew's carnivorous response is not yet known, some studies have begun to shed light on how the plant is able to move in response to mechanical and chemical stimulation to envelop and digest prey. Individual tentacles, when mechanically stimulated, fire action potentials that terminate near the base of the tentacle, resulting in rapid movement of the tentacle towards the center of the leaf. This response is more prominent when marginal tentacles further away from the leaf center are stimulated. The tentacle movement response is achieved through auxin-mediated acid growth. When action potentials reach their target cells, the plant hormone auxin causes protons (H⁺ ions) to be pumped out of the plasma membrane into the cell wall, thereby reducing the pH and making the cell wall more acidic. The resulting reduction in pH causes the relaxation of the cell wall protein, expansin, and allows for an increase in cell volume via osmosis and turgor. As a result of differential cell growth rates, the sundew tentacles are able to achieve movement towards prey and the leaf center through the bending caused by expanding cells.  Among some drosera species, a second bending response occurs in which non-local, distant tentacles bend towards prey as well as the bending of the entire leaf blade to maximize contact with prey. While mechanical stimulation is sufficient to achieve a localized tenta
caption: Emergences of an Australian D. indica
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