EPOW - Ecology Picture of the Week

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The Lichen With Algal Warts

Credit & Copyright:  Dr. Bruce G. Marcot
  

Explanation:  In the photos above, seen under 30x (top photo) and 60x (bottom photo) magnification, is an oddity of the lichen world.  This leafy lichen is known by sundry common names, including common freckle pelt, studded leather lichen, green dog lichen, leafy lichen, felt lichen, and others.  We'll go with "freckled lichen." The species is found circumpolar where it grows in seasonally cold places.  I found this in the high Cascade Mountains of southern Washington state in the U.S.   The "leaves" (thallus) of this species can grow up to 3 feet wide, and are green but turn pale when it dries as with these laboratory specimens.   As you likely know, lichens are an amalgam of fungi and algae. But what are the "freckles?"  They are tiny bodies known as cephalodia ... which are actually nodules of a blue-green alga called Nostoc that we met in a stream in a previous EPOW episode.  The cephalodia "warts" provide nitrogen to the rest of the lichen which consists of fungus and green algae.  And they can fix a remarkable amount of nitrogen, at that, but the rate falls off rapidly in the presence of atmospheric pH under 6.0 ... so its nitrogen fixation rate can be a good indicator of acid rain.   This species also is sensitivity to air pollution, especially sulfur dioxide and flourides, so it's a good indicator of air quality.   Moreover -- get this -- this species also can absorb atmospheric radioactive fallout more readily than can vascular plants ... making it also an indicator of ... I don't want to think about it ...  So this species consists of two forms of algae plus fungi.  Three's company, eh?  Moreover, this lichen apparently also has medicinal properties.  According to one source (MacKinnon et al. 1992), the liquid extracted by boiling this lichen has been used in Scandinavia to treat chapped skin of babies and the feet of adults.   One has to wonder what other functions and uses that this, and related, lichens serve!      The underside of this lichen lacks the blue-green algae Nostoc wart nodules found on the upper side.    Information:      MacKinnon, A., J. Pojar, and R. Coupe. 1992. Plants of northern British Columbia. Lone Pine Publishing, Vancouver, B.C. 352 pp.      McCune, B., and L. Geiser. 1997. Macrolichens of the Pacific Northwest. Oregon State University Press, Corvallis, Oregon. 386 pp.      Vitt, D., J. Marsh, and R. Bovey. 1988. Mosses lichens & ferns of northwest North America. Lone Pine Publishing, Canada. 296 pp.