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Drosera, also known as sundew, is a genus of carnivorous plants that include about 188 known species. Its name is derived from the physical characteristics of its glandular leaf that seemingly glisten like dew in the sun. Sundews can grow in highly humid and sandy soil, even when the soil is lacking in organic nitrogen and phosphorus. To compensate for the lack of nutrients, sundews are known to capture and digest insects by utilizing the surfaces of their leaves, which are composed of mucilaginous glands.
Sundews act like sticky flypaper. They have long, stimulated tentacles on their leaves which easily lure insects. As soon as their prey is captured, the leaf slowly coils around it, which can take minutes or even hours. The tentacles of a Drosera can bend in any direction, but whenever the leaf catches an insect, the tentacles bend the leaf inwards.
The tentacles of a Drosera produce digestive juices that aid in the decomposition of their captured prey. These digestive enzymes include protease and phosphatase, which gradually increase in concentration once the tentacles capture an insect to digest. Other than that, the glands on the tentacles produce attractive nectar and adhesive compounds that can make the insect stick to the leaf until it completely closes down on the prey.
Carnivorous plants such as Drosera need insects to compensate for their poor mineral nutrition. This is because the genus lacks the capacity to obtain such nutrients from the soil where it grows. To survive, they have evolved into carnivorous plants specializing in nutrient intake from above the soil. The pygmy sundew, for example, lacks nitrate reductase, which is a plant enzyme that aids in the digestion of earth-bound nitrates.
As herbaceous plants that are known to achieve a lifespan of up to 50 years, species that belong to the Drosera genus are also considered perennial plants. Some species grow vertically, while the viney and rosette species tend to hug the ground. Sundews can be found in almost every continent except for Antartica.
In tropical countries, some species of Drosera grow all-year-round, much like the pygmy sundews found in Australia, while others die back to their roots during the dry season and reemerge during autumn. The species that grow in cold, snowy habitats coil back to their packed buds, known as hibernacula, during the winter season. Species found in North America and Europe belong to this group.
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