Microbiology

Saprophytes



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Beside the narrow roads at Lassen Volcanic National Park grow plants that look somewhat like tall red hyacinths. That sketchy description doesn't do them justice though; they're gorgeous. They're called Snow Plants. Their scarlet spears stand out vividly against the gray-green pines in the last patches of snow that linger near Mount Lassen until at least June. Because there is no green anywhere on the plant, it's as if a bouquet sprang directly from the cold ground.

Years ago park rangers explained to children that Snow Plants, sarcodes sanguinea, were saprophytes, parasitic plants that lived off rotting organic matter. Botanists no longer believe things work that way. Flowering plants that were once called saprophytes are now called myco-heterotrophs, the scientific term for parasitic plants that live off the food that fungi take from plants that can photosynthesize.

Myco-heterotrophs lack chlorophyll, necessary for photosynthesis, and thus lack the ability to convert water, carbon dioxide, and sunlight into carbohydrates and oxygen. They can't make their own food. Since no plant can, they can't draw carbohydrates directly from the vegetation in the soil. So they live in a community of plants. A green plant produces carbohydrates from sunlight, some of that food goes to its roots, a fungus takes nutrition from the plant roots, and the myco-heterotroph takes nutrition from the fungus. Fungus also lack chlorophyll, and thus can't manufacture food, but their enzymes dissolve food from their host into a solution that can be absorbed. For this reason, plants like the Snow Plant are often called epiparasites, meaning parasites of parasites.

So in many softwood forests of western America, trees benefit from mycorrhyzal (root dwelling) fungus, whose hyphae (filaments) increase the surface area of the tree's own roots, improving their ability to gather water and needed minerals. In exchange, the trees send some carbohydrates to their networks of root fungi. Then, where they are present, the epiparasites take nutrition from the fungus. At our current state of knowledge, it is believed that the fungus is getting nothing from the parasitic flower.

The ghostly Indian Pipes, monotropa uniflora, a fleshy off-white flower found in deep shade and rich soil, is a plant of this type. Many orchids function as myco-heterotrophs, through at least part of their life cycle. Examples include the pale elusive phantom orchid, cephalanthera austiniae, which is found, rarely, in shady forests of the Pacific Northwest from British Columbia down to California. In forests across the country grow various species of the coral root flower, also a native orchid.



These plants would obviously be extremely hard for a home gardener to cultivate, because their growth requirements are so complicated. An entire plant community would have to be constructed for the epiparasitic plant to survive. How beautiful though, to come upon them in the deep woods, or, as in Lassen, to see them growing by the road, surrounded by snow.



http://botit.botany.wisc.edu/toms_fungi/oct2002.html
http://encyclopedia.farlex.com/saprophyte
http://www.answers.com/topic/fungus?cat=entertainment
http://www.geog.ubc.ca/~brian/phantomorchid.htm
http://dawson.nu/indian-pipes.html
http://www.nps.gov/lavo/

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