General Topics

Lichens of Missouri

What is a Lichen?

Lichens are generally considered both algae and fungi. They have the green quality from algae, as well as the ability to grow without seeds from the decomposition of water (Marshall). Additionally, they are similar to fungi because in some instances, instead of creating their own food-like other plants-they have fine threads called “hyphae” which acquire nutrients from the tree or rock they are growing on or the algae they grow with (Marshall). The grey/green color of the lichen is because there is a green layer of plant covered by a white layer (Marshall). When the air is moist, the white layer becomes more translucent from the moisture, allowing the green color to stand out more (Marshall). The algae are very skilled in capitalizing on moist environments when they exist, and in this way, it provides nutrition to the fungi (Marshall). The fungi can protect the algae when the air is drier, in order to create a true mutualistic relationship (Marshall). The relationship between these two organisms can be reproduced artificially by allowing a fungus to grow on an already sufficiently growing alga (Marshall). Each new fungus and alga combination create a new type of lichen. Usually, these lichens all have the capability of being successful new organisms (Marshall). Therefore, a lichen is not actually an individual organism, but rather a mutualistic relationship between two organisms.

Why do Lichens Matter?

Lichens are important because they are examples of symbiotic evolution. Not only are lichens themselves a combination of two organisms (algae and fungi) in a mutualistic relationship, their relationship with trees (if they are the substrate) is commensalism. Also, lichens have their own microbiomes and participate in a mutualistic relationship with those bacteria. Thus, they fill an important niche in their ecosystem, big and small, and

Furthermore, Lichens are very sensitive to pollution and poor air quality (“Lichens and Air Quality”). This means that they are good indicators of air quality depending on which lichen species growth there (“Lichens and Air Quality”). In many ways, this is due to the few lichen species that can survive the harsh conditions (“Lichens and Air Quality”). Thus, lichens deserve our attention because they are one of the many organisms that are impacted by our emissions.

Three Classes of Lichens

Crustose Lichens

Appearance: The crustose lichens generally look very crusty, as their name suggests, and are often very flat.

Attachment to the surface: The whole thallus touches the surface so that the entire organism is pushed against the rock, tree, bark, etc. it resides upon.

Foliose Lichens

Appearance: The foliose lichens often resemble leaves or discolored petals.

Attachment to the surface: A very minimal part of the thallus is attached to the substrate, so the edges of the lichen curl upwards to make the distinct foliose shape.

Fruticose Lichens

Appearance: The fruticose lichens are unique in their bushiness, and the way their thalli resemble branches and stalks (Thomas 9).

Attachment to the surface: The thallus is only attached to the surface at the bottom of the stalk, so the structure is more three dimensional and the lichen is denser in the space it occupies off of the substrate.

Common Types of Lichens

Reindeer Moss (cladina subtennius)

This species actually carries a misnomer, as it is really a Lichen. The thalli are smooth thin stalks with branches twisting off of them (Thomas 104). When observed after a heavy due or in high humidity, the lichen will be spongy in texture. But when the air is dry and the lichen lacks moisture, the lichen will be brittle and more susceptible to breakage. Reindeer moss is a fruticose lichen, which makes sense because the thalli look like mini trees! This is why Reindeer moss is sometimes used to represent trees on architectural models (Thomas 105).

photo taken by Maggie Newberry

Rock Tripe (Dermatocarpon)

This lichen is foliose in character because its thin white-grey thallus is only attached to the rock in its center. The edges can curl up and break, making it look like a type of leaf or petal. The grey dots on the thallus are fruiting bodies and are characteristic of the species. This can often be found in areas with moisture and are usually found growing on rocks or rocky bluffs (Thomas 112).

Shield Lichen (Parmelia)

photo taken by Maggie Newberry

Blister Lichen (Physica Stellaris)

The Blister lichen is so called because the small uneven thalli each resemble a blister with a black center on surrounded by a lighter grey “skin” (Thomas 116). These lobes overlap randomly and generally grow flat against the tree, closer to the canopy (Thomas 116). I was not able to observe this lichen myself, mostly because it is generally not located on the base of the tree or on rocks.

Candelaria Concolor

The name of this lichen means “uniformly glittering like a candle” because it is either bright yellow-green in color “resembl[ing] a fine spray of yellow paint splatter” (Thomas 117). This is a foliose lichen, with very fine branches as the thalli, and generally grows on trees or their bark rather than rocks (Thomas 117).

Xanthoria Candelaria

Similar to Candelaria Concolor, the name of this lichen means “glittering like a golden candle”, and it is also a foliose lichen (Thomas 118). Both have small thalli, with “branching lobes”, but Xanthoria is known for it’s yellow-orange hue, whereas Candelaria is characteristically yellow-green (Thomas 119).

Acarospora (Small Spores)

This lichen’s thallus is packed against the substrate, which makes it a crustose lichen (Thomas). Although it can be difficult to identify because many crustose lichens look alike, distinguishing factors include the thallus being divided into smaller sections by cracks and the “white to greenish-gray to brown” (Thomas).

photo taken by Maggie Newberry

photo taken by Maggie Newberry

Combinations of Lichens

When observing lichens in the field, often times speices and categories of lichens overlap. This is because lichens are not made to be one species, because each new combination of fungi and algae has a different resulting lichen. Below are some photographs of observed lichens embodying characteristics of multiple species.

photo taken by Maggie Newberry

photo taken by Maggie Newberry


Lichenometry is used by geologists and archaeologists in order to create an accurate timescale when studying rocks or artifacts found in the field.  It is a “useful tool to date past events when surface ages are unknown” (Shanteau).  Recently, there has been an uptake of “Rhizocarpon chrysoleuca” as a replacement for the more commonly used species “Rhizocarpon geographicum” (Shanteau).  Rhizocarpon geographicum has been used universally in the field of lichenometry in the past because it is well studied and found everywhere (Shanteau).  However, the turn towards chrysoleuca is increasing the capabilities of this field by allowing new references to be used. This is important because lichens grow so slowly, which is why they are used in dating, that they cannot be manufactured in a lab if the timescale is to be acquired accurately.

Microbial Ecosystems on Lichens

Not only are lichens an embodiment of symbiosis themselves, the bacteria that grow on them also are an example of this mutualism. They can range from single colonies to films covering the lichen surface (Cardinale et al). The bacteria contribute to the mini-ecosystem by decomposing matter, obtaining nutrients and functioning as biological control agents (Cardinale et al).

An interesting study was conducted in 2012 by Massimiliano Cardinale et al, which studied the causes of variation in the structure of the bacterial communities on different lichens. The observed factors for each Lichen were “the ratio between the volume and the weight of the lichens, defined as Delta volume method…the effect of lichen intrinsic (lichen species, thallus age, differentiated thallus parts, growing type) and extrinsic environmental factors (sun exposure and substrate)” (Cardinale et al). They used Fluorescence in situ hybridization (FISH), which allows for microscopic analyses of specific areas on the lichens, in order to observe the variation of “the taxonomic structure of the bacterial communities in lichens” (Cardinale et al). The results illustrated an interesting pattern: “the lichen species does not exert an exclusive effect on the overall community structure”  but this does not mean that different lichens don’t have different “bacterial communities at the species/strain level” (Cardinale et al). Essentially, the only factors that impact the bacterial structure, other than relative age of the parts of the lichen, are extrinsic factors such as sun exposure and substrate type.

Relative age matters because the young healthy areas have a stable and consistent bacterial community, but the old decaying areas vary in the bacterial community and lack consistency. This is probably because the bacteria on the younger parts are anabolic and help build up the matter of the lichen, and the bacteria on the older parts are “catabolic sinks” and they break down the decaying biomass either to replace into the substrate of for the lichen to use in its growth (Cardinale et al). Therefore, lichens as individual organisms and how they fit into ecosystems are a great example of symbiotic evolution.

Symbiosis and its Categories

Symbiosis is when at least two organisms live in close proximity, and at least one benefits from the relationship. Therefore, symbiotic evolution would be when these species change over generations in order to adapt to the symbiotic relationship. Symbiosis is comprised of three more specific categories: mutualism, commensalism, and parasitism (Nelson). Mutualism is when both/all organisms in the relationship benefit, commensalism is when one benefits but the other is not harmed, and parasitism is when one benefits and the other is harmed (Nelson). Each of these types of relationships can constitute symbiotic evolution because evolution is dictated by what is advantageous to a species. For mutualism, both species would evolve so that the relationship would continue to each’s advantage. For commensalism, one species would evolve to continue the relationship because it is advantageous, and the other would have no preference. For parasitism, the parasite would evolve to continue the relationship because it is advantageous, but the other species would evolve to discontinue the relationship because it is disadvantageous. Lichen’s themselves embody mutualism, and if they grow on trees, they also demonstrate commensalism.

Miniature Field Guide

Works Cited

“Lichens and Air Quality.” , National Park Service, 27 Dec. 2017.

Marshall, Nina L. Mosses and Lichens. New York, Doubleday, Page & Company, 1907, pp. 3-7.

Nelson, Daniel. “Mutualism, Commensalism, Parasitism: Types Of Symbiosis With Examples.” Science Trends, 6 Feb. 2018.

Shanteau, Jennifer, and Casey D. Allen. “Rhizoplaca Chrysoleuca as an Alternative Lichenometric Species: A Preliminary Investigation at the Lawn Lake Alluvial Fan, Rocky Mountain National Park, CO USA.” Geographical Bulletin 58, no. 2 (November 2017): 79–91.

Thomas, Lisa P., and James R. Jackson. Walk Softly Upon the Earth. Conservation Commission of the State of Missouri, 1985.

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