Symbiotic heterotrophs are plants that benefit from a mutual life together. There are two types of symbiosis: endosymbiosis, where one plant lives within another and ectosymbiosis, where one plants lives on another. The algae and fungus that form lichens are a common form of symbiosis. The algae makes the food both plants need, while the fungus provides water and minerals.
All plants fall into one of two categories -- autotrophic or heterotrophic. Autotrophic plants survive on the simple molecules produced during photosynthesis. Most plants are autotrophic. Heterotrophic plants require more complex molecules that have already been processed by another life form. Heterotrophic plants may be symbiotic, parasitic or carnivorous.
Parasitic heterotrophs are plants that rely on a host for nutrition. True parasitic plants, such as dodder, must rely on a host for all of its nutritional needs. Semi-parasitic plants, like mistletoe, can produce chlorophyll but do not have the root system to draw up water and minerals. Both types of parasites use root-like suckers to draw sap from the host plant.
Carnivorous heterotrophs are capable of photosynthesis but live in environments that require a nitrogen supplement supplied from living creatures. The approximately 600 species of carnivorous plants survive on insects and small mammals. Bladderworts, which account for half of carnivorous plants, rely on aspiration to trap prey. Prey animals are sucked (or aspirated) into a small sac, where they are slowly digested. Sundews make up one-third of carnivorous plants and use mucilage to trap prey. Insects are attracted to and become stuck in a sticky nectar, allowing the plant's digestive glands to close around the insect for digestion. There are believed to be 100 types of pitcher plants, which use pitchers filled with nectar and rain water to trap their prey. Insects and small mammals are attracted to the water and fall into the pitcher where they are digested. Two types of hinge plants are known to exist. A fly trap attracts prey with nectar then ensnares its prey within hinged leaves. The trapped insect is unable to get away and is digested.
The variety of heterotrophic plants allows them to survive in a wide range of environments. The marshes of North and South Carolina are the native home to fly traps, while pitcher plants prefer tropical habitats, such as Australia, Madagascar and Sri Lanka and boggy marshes such as the northwestern United States and England. Sundews thrive in both temperate and tropical environments, including Morocco, England and the United States. Parasitic plants range from the northwest United States to northern South America, Mexico and Asia. Symbiotic plants are the hardiest of the three varieties of heterotrophs and they thrive in regions where other plants could not, including the Antarctic and the deserts of Saudi Arabia.
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