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Parasitic Flowering Plants (2)


Flowering plants that live on other plants. Stem parasites. Root parasites.


When one organism steals all of its food from another organism's body it is called a parasite. The organism who is being robbed of its food supply is called the host. The parasitic mode of existence can be found throughout the kingdoms of life, from bacteria and fungi to insects, arachnids and worms. Parasitism has also evolved in many families of flowering plants. Some heterotrophic flowering plants get their nutrition from mycorrhizal soil fungi that are in turn attached to the roots of forest trees. These interesting plants are called mycotrophic wildflowers or mycoheterotrophs and are discussed in another article called fungus flowers. True plant parasites can be hemiparasitic with photosynthetic leaves (such as mistletoe), or holoparasitic and completely dependent on their host (such as dodder). Some stem parasites, such as a local southern California desert native, are endoparasitic and live completely within the stems of their host. The only part of Pilostyles that emerges from the host is a tiny bud that opens into a minute red flower. This is similar to a pimple appearing on your face that bursts into a tiny blossom. Of all the more than 230,000 species of flowering plants, the root and stem parasites certainly include some of the most bizarre and beautiful species; including the world's largest flower that is three feet (one meter) in diameter.

Three common parasitic genera of stem parasites in California include the mistletoes Phoradendron and Arceuthobium of the Mistletoe Family, and dodder of the Morning-Glory Family. The European mistletoe has also been found in northern California on maples, alders, elms, willow, and other deciduous trees. Probably the most widespread mistletoe in California is Phoradendron, a name derived from two Greek words meaning "tree thief." Some species, such as oak mistletoe, have oval, green leaves (the decorative kind used at Christmas), while other species, such as desert mistletoe have inconspicuous scale-like leaves. The genus Arceuthobium also has small scale-like leaves and commonly grows on cone-bearing trees. It is often called dwarf mistletoe or pine mistletoe.
Different species of mistletoe typically grow on different species of host trees and shrubs. For example, desert mistletoe commonly grows on cat-claw acacia, although it may also grow on other desert shrubs. Desert mistletoe produces juicy, bright red berries that provide numerous birds with food and water during the winter months. If you walk along a desert wash in the Colorado Desert region of the southwestern United States, you can often spot a black bird called the phainopepla near clumps of mistletoe. This bird is easy to identify because of the conspicuous crest on its head. Mistletoe seeds are covered with a glue-like substance that sticks to the bills of birds. When birds try to clean their bills, the seeds adhere to the limbs of other trees and shrubs. The seeds also pass through the bird's digestive tract and are transported from one bush to another in the bird's droppings. In fact, this probably explains the derivation of the word mistletoe: from two Germanic words: mista (dung) and tan (twig); referring to bird droppings on a branch or stem. Apparently when the word mistletoe was first used in Europe, people were already aware of the dispersal of mistletoe seeds by birds. ...

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Tinklalapyje paskelbta2005-06-19
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