Around the Garden *

One of the most frequent questions I have heard from tree-lovers is “What is this green stuff that’s killing my tree?”  The phenomenon in question is lichen, and it really is an amazing part of our natural world. And trust me, this is not a tree-killer.

Lichens are those flat, often circular, slightly furry patches that show up on your trees and, sometimes, on rocks as well. Botanically, they are a symbiotic combination of a fungus and either an alga, a cyanobacterium, or both, which give the organism its characteristic blue-green-gray coloration.

At right and below, blue-green lichen grow on sugar maples and on a Japanese maple.

 Often, they appear on dying trees, and people assume the lichens are the cause. Typically, lichens are simply opportunistic, and grow in damp and shady places. These just happen to be the conditions in which some trees will decline, while lichen thrive. Unlike fungi on their own, lichen do not need to absorb decaying material, because the algal or cyanobacterial component is photosynthesizing, something that a fungus on its own does not do. Photos below show lichen growing on asphalt, on a rock and on a chunk of a mulberry tree.

Scientists, in fact, consider many lichens to be bio-indicators of clean air, since they do not grow in areas with extreme air pollution. Oddly, they are a food source for elk, who scrape them off rocks to eat them. Lichens have been used for dye as well.

As with many fungi, lichens’ actual structure and life processes were not well understood by science for hundreds of years. It was a nineteenth-century Swiss botanist who first discovered this “unnatural” marriage across kingdoms, although at the time of his discovery, fungi were still considered part of the plant kingdom.

It is not surprising that these modest plants escaped serious inquiry, since they are harmless and rarely a food source. Fungi, too, have mysteries that have only begun to be unraveled recently. DNA research has allowed identification of genetically identical strands of fungal mycelia penetrating hundreds of acres, creating what some scientists consider to be among the earth’s largest organisms.  

A lecture on lichens will be presented on April 17 at the Kellogg Environmental Center in Derby. This joint presentation by the Naugatuck Valley Audubon Society and the CT Department of Energy and Environmental Protection will take place at 7:30 pm, and is appropriate for adults and children over 10. A small admission fee will be charged.

* Absolutely devoid of April Fool's content, just in case tongue in cheek humor really freaks you out!