What's to Like About Lichen

March 13, 2018


Photographer: Patti Weeks 
Summary Author: Patti Weeks 

One of the oldest, hardiest and most widespread living organisms, first appearing approximately 400 million years ago, lichens have at least 13,000 identified species worldwide. This photo, taken near Rhinebeck, New York on December 24, 2017, shows two of the three main categories of lichen: crustose, flat, two-dimensional, firmly attached and crust-like; and foliose, leaf-like with distinct upper and lower leafy surfaces. The other group, fruticose (not shown in this photo), is tube-like with branched stems. Note that the dark green moss in the photo is a completely different species.

Lichen presents a symbiotic partnership between two or more dissimilar organisms, creating a vegetative body called a thallus. About 80 percent of the lichen is composed of fungus, which provides physical structure, and absorbs moisture and minerals. The other life forms of green algae and/or cyanobacteria provide food to the thalli through photosynthesis.

Growing best in areas with light, moisture and moderate temperatures, lichens can be found on the surfaces of rocks, trees and soil, and also on manmade wooden, stone or metal structures. Lichens promote both physical and chemical weathering of rock, but are non-parasitic and so will not harm healthy trees.

Besides bestowing beauty, lichens can provide a food source for some animals, such as flying squirrels and reindeer. Birds use them in nest making. A decline in lichens can be an indicator of increasing levels of air pollution. Lichens have been used to estimate dates of past geologic events, such as the advance and retreat of glaciers. We’ve used them for making medicines, and dyes for yarns and fabrics. Some cultures have used lichens in their diets, but be warned — the ones with cyanobacteria are poisonous!

Photo Details: Camera: SONY DSC-HX400IV camera; 20.68 mm focal length; f/4 aperture; 1/250 exposure; ISO 160.