Likin’ lichen

I am of the opinion that lichens are very interesting creatures. Consider that members of the group have existed for more than 400 million years, while conifers have been around a mere 250 million years and the flowering plants came on the scene a scant 150 million years ago. Lichens are even more ancient than mosses and ferns which are known from approximately 350 million years ago. Lichens live what can only be described as a tenuous life. Although some may be found in extreme environments such as tundra and desert, most live a quiet existence in more temperate environments, growing as epiphytes and covering the surfaces of trees, rocks, and soils. Lichens are unusual in that they represent the symbiotic union of an alga and a fungus. Algae are photosynthetic and are able to fix atmospheric carbon into sugars in support of themselves and of the fungal partner with which they live. For its part, the fungus provides protection for its algal symbionts and acts to take up water and mineral nutrients in support of algal growth and metabolism. Some lichens may be quite colorful, most are not however and may go unnoticed. Although inconspicuous, lichens are important ecological players in the process known as primary succession. Because they are able to live and thrive under very dry and nutrient-poor conditions they are some of the first organisms to colonize open substrate when it becomes available. Once lichens become established, their presence can modify harsh environmental conditions thereby facilitating the immigration of other sorts of colonizing species, and thus the sequence known as secondary succession may proceed apace. I also appreciate lichens because many act as indicators of environmental quality. They are living biomonitors much like the proverbial Canary in the Coal Mine. As it happens, lichens are particularly sensitive to sulfur dioxide and to acidified rain water. Different species show different tolerances to airborne pollutants so one can gauge air quality by a census of the lichen population in a particular area. And, finally, because lichens are adapted to live in nutrient-poor situations, they grow very slowly, perhaps just 0.1 – 10 mm per year. So, the next time you’re out for a stroll through the woods or for a hike up a hill, keep an eye out for these very pretty, very living, things and step aside.

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