British soldier lichen

Lichens

What exactly are they?

To put it simply, lichens are organisms composed of a fungal and a photosynthetic element (either algae or cyanobacteria or sometimes both!). More specifically, lichen forms a symbiotic relationship between its fungal component and its photosynthetic component. In this relationship, the photosynthetic component provides a food source by utilizing light energy, and the fungal component makes up the bulk of its structure and provides habitat, water, and nutrients for its photo-symbiont. This interaction is known as a mutualistic symbiotic relationship because both organisms benefit.

Lichens are unique in that they look like plants but are not all that closely related. Given their appearance, it is no surprise that lichens are often confused with mosses and other bryophytes. However, lichens are very different biologically and are only really related to bryophytes through their photosynthetic component. The fungal component? It is actually more closely related to we humans than it is to plants. Combine this with the fact that the largest bulk of lichens are made up of their fungal component (via interconnected threads called hyphae); we can see how these species are not closely related to the rest of the plant kingdom.

The fact that a lichen is not actually one organism but rather two or more melded together is a characteristic unique to them as well, making them exceptionally adaptable and allowing them to inhabit many diverse and harsh living conditions. Because of these features and their ability to break down substrate, lichens are often key components in creating soil in barren areas.

Although it is common to see some lichens in urban areas, if you are looking for a wide variety and abundance of lichen on Prince Edward Island, areas far from the city are your best bet. The most extensive breadth of lichen can be found in old growth forests far from pollution and with high humidity. Their typically low tolerance for pollution makes lichens excellent indicator species – an ecological canary-in-the-coal-mine if you will.

Lichens are a truly remarkable and diverse group of organisms, with upwards of 2,000 different species in North America alone. To make identification more manageable, it is easier if we consider lichens based on their three different growth forms: Foliose, Fruticose, and Crustose, or, as I like to call them: Leafy, Hairy, and Crusty.

Foliose Lichens (Leafy)

Of the three types, Foliose lichens are perhaps the most plant-like in appearance. This is due to their lobular growth form. These lobes can sometimes appear to be “leafy” as the thallus are typically broad and flattened. They are often loosely attached to their substrate and have clearly distinguished upper and lower surfaces. The shape, length, and width of these lobes are how you can distinguish lichens in this grouping from one another.

Hammered Shield Lichen (Parmelia sulcata)

The Hammered Shield is a common form of lichen on Prince Edward Island. Next time you sit on an old picnic table or park bench watch for a gray, leafy-looking structure growing flat against the wood. Almost all older wooden structures will have this lichen as well as many trees. However, despite its everyday appearance, hammered shield lichen is perhaps best known for its use in hummingbird nests, where they are used to encompass the nests in an armour-like manner.

Lung lichen (Loberia pulmonaria)

Lung lichens consist of members from three different kingdoms, a combination of fungi, green algae, and cyanobacteria all in one symbiotic organism. Lung lichens are bright green when wet but turn brown and papery under dry conditions. They prefer moist, coastal areas and old growth forests. In PEI, you can find this lichen residing on the bark of maple and oak trees. Because this lichen has an affinity for older trees, its prevalence and abundance are often used to help indicate a forests age. This lichen is becoming more and more rare around the world as forestry and pollution quickly displace it. That is why organizations such as ours at Macphail Woods are so important, not just for plant species but for other organisms that rely on forests for habitat as well.

Fruticose Lichens (Hairy)

Fruticose lichens are highly branched and fibrous. When cut, they yield a thin round cross section and have no distinction between upper and lower surfaces. These aspects often give them the appearance of being hairy, although not all species necessarily look this way. You can often find fruticose lichen at the bases of trees, draped over tree branches, or even hanging off telephone wires. Fruticose lichen either hang upside down or have unique structural characteristics that allow them to stand erect. It is these supporting structures that are often used to distinguish one fruticose lichen from another.

British Soldier Lichen (Cladonia cristatella)

One of the exceptions to the “hairy” rule is the British Soldier Lichen. These are perhaps some of the best-known lichens for their bright color, unique appearance, and prevalence throughout most of the eastern half of North America. They earned their name due to their distinctive red tops which resemble the hats worn by British soldiers during the American Revolutionary War. They stand erect in decaying wood and at the bases of trees and have a grey-green lower half. They are adept at breaking down old wood and provide lots of nutrients for the soil (particularly nitrogen).

Old Man’s Beard (Usnea spp.)

Old Man’s Beard is a relatively common lichen on P.E.I. You can see it often hanging from spruce trees and should have no problem identifying it as its name is an excellent description of its appearance. Its fibrous gray-green vegetative structure hangs loosely from trees and accurately resembles the beard of a weathered old man. Despite its prevalence in many areas, Old Man’s Beard is highly sensitive to air pollution so you may have to travel away from urban areas to find it. An interesting fact: Old Man’s Beard lichen was used during war times as a bandage because of its potent anti-fungal and antibiotic properties. It was extremely helpful for wounded soldiers who were without access to medical care as it was often readily available and protected wounds from disease. Its fibrous structure is ideal for covering wounds while still allowing air to access the wound to speed healing.

Crustose Lichens (Crusty)

Crustose lichens form rough textured crusts over a substrate. The lower surface of these lichens grows amongst the substrate particles, meaning that the lichen cannot be separated from the substrate without destroying parts of it in the process. These lichens are often present as brightly colored patches on trees or even brick walls; however, there are some that can only be distinguished using a magnifying glass. These lichens grow very low to the substrate surface and are typically characterized by what substrate they grow on and how they interact with that substrate.

Sulfur Firedot Lichen (Caloplaca flavovirescens)

This lichen is bright brown-orange in color and grows well on limestone or sandstone in coastal areas such as PEI. You may also find this lichen adorning stone or concrete structures. Like all crustose lichens, this species forms a crusty layer over a substrate and cannot be removed without taking some substrate with it.

Rusty Brook Lichen (Ionaspis lacustris)

As is the trend with most lichen, the name of this species is indicative of its characteristics, as it is a rusty orange color and is found in or around streams, lakes, and brooks. Any rusty orange patches present on stream-side rocks will almost always be Rusty Brook Lichen. It is unique in that it is adapted to survive periodic submersion in fresh water, as the rocks it resides on are submerged by increased water levels, waves or flooding events.


As you scroll through our guides, you’ll notice some guides have more information or better photos than others. We are always looking to increase the quality and accessibility of our nature guides.

If you are interested in helping us improve these guides, whether through photos, research, writing or website development, then please contact us via phone: (902) 651-2575 or email: danielmcrae@macphailwoods.org

A big thank you to Jenna Marie Cahill for contributing this nature guide.

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