Lichens are fascinating organisms that often go unnoticed, but they play significant roles in various ecosystems. The English word lichen derives from the Greek λειχήν leichēn (“tree moss, lichen, lichen-like eruption on skin”) via Latin lichen.
Lichens are unique because they’re not just one organism, but rather a symbiotic relationship between fungi and either algae or cyanobacteria[1]. The fungus provides a protective structure and absorbs nutrients, while the algae or cyanobacteria photosynthesize and provide food for the partnership.
This relationship forms the thallus, which is the body of the lichen. Lichens come in various forms, including crustose (crusty), foliose (leafy), and fruticose (shrubby), each with its own distinct structure. Lichens are not just gray, drab, crusts.
Actually, lichens come in a rich variety of colors, ranging from bright yellow, red, and orange to green, black, brown, silver, and gray. Lichens are incredibly resilient organisms. They can survive in extreme environments, from icy tundras to arid deserts.
This resilience is due to their unique physiology, which allows them to withstand drought, high radiation levels, and even pollution. Lichens play crucial roles in ecosystems. They contribute to soil formation by breaking down rocks and releasing minerals. Additionally, they provide habitats and food for various organisms, such as insects and small mammals.
Taxonomists estimate that between 17-30% of all fungus species are capable of becoming lichens. With the number of fungi species believed to number over 1.5 million, there may be at least 250,000 lichen species. Since many fungi look alike superficially, taxonomists have resorted to genetic analysis to differentiate species.
In a 2014 study, what was assumed to be one species of lichen (Dictyonema glabratum) turned out to be 126 genetically distinct “species”. Based on records from the Consortium of North American Lichen Herbaria[2] website (www.lichenportal.org) the lichen flora of Arizona consists of 969 species, or about 19% of all lichen taxa known in North America. Lichens are also indicators of environmental health,
as certain species are sensitive to pollution levels. Lichens have a remarkable ability to absorb water from the atmosphere. When moisture is available, lichens become hydrated and metabolically active. However, they can also survive long periods of drought by going into a dormant state until water becomes available again. Lichens produce a wide range of metabolites, including acids, pigments, and antibiotics.
These metabolites have various functions, such as deterring herbivores, protecting against harmful microbes, and even providing potential medicinal properties. Lichens are generally slow-growing organisms, with growth rates ranging from a few millimeters to a few centimeters per year,
depending on environmental conditions. Some lichens can live for centuries, with some even reaching thousands of years old. Lichens reproduce both sexually and asexually. In sexual reproduction, fungal spores combine with algal or cyanobacterial cells to form new lichens.
Asexual reproduction occurs through fragmentation, where pieces of the lichen break off and establish new colonies elsewhere. Dispersal typically occurs through wind, water, or animals carrying lichen fragments to new locations. Throughout history, humans have used lichens for a variety of purposes including for clothing and decoration, and even for eating. Lichens are used today in toothpastes, deodorants, salves and other products and are researched for their antibiotic properties.
Footnotes
- Cyanobacteria are aquatic and photosynthetic, that is, they live in the water, and can manufacture their own food. Because they are bacteria, they are quite small and usually unicellular, though they often grow in colonies large enough to see. They have the distinction of being the oldest known fossils, more than 3.5 billion years old, in fact! It may surprise you then to know that the cyanobacteria are still around; they are one of the largest and most important groups of bacteria on earth. [Back]
- The Consortium of North American Lichen Herbaria (CNALH) is a collaborative network comprising multiple herbaria across North America dedicated to the preservation, study, and dissemination of lichen specimens and associated data. Established to facilitate communication and cooperation among institutions and researchers interested in lichenology, CNALH serves as a central hub for accessing lichen specimen information, including images, metadata, and literature references. By fostering collaboration and providing access to a wealth of resources, CNALH plays a crucial role in advancing scientific knowledge and conservation efforts related to lichens in North America. [Back]
Further Reading
Sources
- Wikipedia “Lichen” https://en.wikipedia.org/wiki/Lichen#Taxonomy_and_classification
- Arizona state University – Biodiversity Knowledge Integration Center “Ten Things You Might Not Know About Lichens, But Wish You Did” https://biokic.asu.edu/ten_things_about_lichens
- Deschutes Land Trust “Five fun facts about lichen” https://www.deschuteslandtrust.org/news/blog/2016-blog-posts/five-fun-facts-about-lichen
- UCMP Berkeley “Introduction to the Cyanobacteria” https://ucmp.berkeley.edu/bacteria/cyanointro.html
- Consortium of North American Lichen Herbaria. “About CNALH.” Accessed January 25, 2022. https://lichenportal.org/cnalh/about.php
