January 4, 2023
This time of the year I become obsessed with the plants and other organisms that thrive during the wet and cold time of the year. Looking at the bare branches of the trees one can see a light sage-green fuzzy looking organism that looks like a plant, and erroneously is often called a moss. These are a group of organisms called Lichens which are not considered to be a plant or an animal. They can resemble hair-like structures, hang down more than several feet in length, or form tight clumps and flattened bumps along the bark or branches. Lichens are, according to Stephen Sharnoff who wrote the Field Guide to California Lichens, a “specializedfungi that have become “lichenized” teaming up with a photosynthetic partner that lives inside them. This partner, called a photobiont, is most often a species of alga, but in some lichens, it is a colony of cyanobacteria and when the fungus becomes “lichenized” it forms an entirely new structure called a thallus.” This relationship between the fungus, alga, and cyanobacteria is considered a classic example of symbiosis. The fungus provides the structure, and the photosynthetic alga and cyanobacteria provide the food.
The many and varied forms of lichens are one of the most fascinating things about them. Sharnoff says that “the shapes of lichens seem to resemble those of coral more than they do of plants.” He reminds us “that the partnerships that fungi form with algae and cyanobacteria are strangely analogous to those found in coral, in which tiny, colonial animals live in symbiosis with algae.” Different groups of lichens are classified by the form of growth each has, either Foliose, Fruticose, Crustose, or Squamulose. Foliose lichens are leafier and longer hair-like structures, and fruticose lichens are shrubby, with either pendant or stubby erect growth. Crustose lichens are flattened and attached strongly to the substrate they are growing on. Lastly squamulose lichens have tiny, crowded, often overlapping lobes called squamules. A hand lens can help you to identify different species and enter into this fantastic world of lichens. Closely related lichen species need further analysis and must be chemically differentiated.
Lichens have been compared to canaries in a coal mine because of their sensitivity to pollution and to environmental change. A lichen absorbs most of its mineral nutrients from the air and rainfall, so pollution from the atmosphere can be especially dangerous to them as they retain and accumulate deadly amounts of heavy metals, sulfur, radioactive elements, nitrogen dioxide, and ozone.
Prior to the 1967 Clean Air Act, finding lichens in the Midwest was difficult, but today they are abundant. They are considered a component of the Forest Ecosystem Health Indicators that are monitored by the U.S. Department of Agriculture Forest Service nationwide. Lichen diversity and species richness is commonly used as a general indicator of forest health and ecological function because they have been found to be key primary producers with important linkages to nutrient cycling and forest food webs. In California, they are also highly valued ecological indicators because of their sensitivity to a wide variety of environmental stressors such as air quality and climate change. Lichens are not indicators of tree disease or lack of health. They are epiphytes, which lack roots so they do not get nutrients from the plant they are growing on.
There are about fifteen hundred species of lichens in California and if you start with the ones in your backyard (probably all over the ground from the latest wind and rainstorms) you will get to know the more common species. Take some time to look closely at them and you will soon find yourself observing them everywhere you go!