I�m not sure what to do with the erratic weather we�ve been experiencing recently � warm, then icy cold, then warm again. A friend posted a photo of a spotted salamander roving around, presumably thinking it�s spring and time to go spawn in a vernal pool somewhere � the salamander is as confused as I am. But one thing I particularly enjoy about these wet rainy winter days is the chance to go outside and look at lichens and mosses. Their colors become much more vibrant after a rain, and those brilliant greens contrasting with the monochrome landscape of winter are lovely to see.

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The windy days last week brought down a large number of branches coated with lichens, ones that are not always easy to see - affixed as they are to branches high up in the trees. I�m referring, in particular, to the so-called beard lichens (they belong to the genus Usnea) - stringy lichens that often do look like beards dangling from high up on branches, trying to get a share of the limited light in a forest.

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Lichens are complex and beautiful, a composite organism, a symbiotic relationship between a fungus, algae and sometimes a cyanobacteria (what used to be called blue-green algae). The fungus provides a protected environment for the algae or cyanobacteria, which, in return, provide energy for the fungus through photosynthesis.

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Lichens in the genus Usnea are typically either upright and shrubby or hanging and filamentous. They�re usually gray-green in color. The green comes from their photobiont (scientific shorthand for photosynthetic symbiotic algae and/or cynobacteria), which in the case of Usnea appears to be a species of green algae. Usnea is a commercially important lichen because it produces an antibiotic chemical (usnic acid) that can kill the bacteria responsible for both strep throat and staph infections. Humans have known about the medicinal properties of Usnea for thousands of years, routinely using Usnea lichens to staunch wounds. Today, thousands of pounds of Usnea are harvested each year for use in antibiotics and deodorants.

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According to Tania Aebi (�Old Man�s Beard� published in Northern Woodlands, June 2006) the way to distinguish Usnea from other similar lichens is �to hold a strand in your fingers and gently tug on either end. The outer green sheath will split, revealing a white inner pith that will stretch before snapping. Usnea is elastic; other lichens aren�t.�

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Try not to overlook lichens; they are the dominant vegetation in some of Earth�s most extreme places: mountaintops, sea-splashed cliffs, and gravestones. If you do any hiking in the White Mountains, you�ll find Usnea well above treeline growing on the stunted trees that are continually blasted by winter winds, frozen into eerie shapes, coated with rime ice, subjected to temperatures well below zero degrees. You�ll also find them along the coast, clinging to salt spray-soaked pine trees, bearding cedars and other evergreens in bogs and swamps. Just appreciate them, don�t collect them - they are slow growing and can be many years old.

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There is some debate as to whether a lichen is a single organism or whether it is an ecosystem of closely interacting life forms. The symbiosis (close association) benefits the fungal partner the most, so it has been proposed that a lichen is really a fungus that has developed agriculture, that it "cultivates" the algae or cyanobacteria in the same way that we grow crops for food. I love this idea; that, blown down from the top of some pine tree, this little tuft of life that I hold cupped in my hand is a complex ecosystem, an entire world.

Susan Pike, a researcher and an environmental sciences and biology teacher at St. Thomas Aquinas High School, welcomes your ideas for future column topics. She may be reached at spike3116@gmail.com. Read more of her Nature News columns online. http://www.seacoastonline.com/topics/Nature-news