On today’s show we learn about the Smooth Horsehair Lichen, a critically endangered lichen native to northeastern North American, specifically maritime Canada.
Rough Transcript
Intro 00:05
Welcome to Bad at Goodbyes.
On today’s show we consider the Smooth Horsehair Lichen
Species Information 02:05
The Smooth Horsehair Lichen is a critically endangered lichen native to northeastern North American, specifically maritime Canada.
Smooth Horsehair Lichen is part of the Bryoria genus, a group of lichen known for their thread-like appearance, hence the name “horsehair.” It is a pendant fruticose lichen. Pendant meaning that it typically grows hanging from the surfaces it lives on. And fruticose, meaning it has a shrubby or hair-like appearance.
This species is an epiphyte on coniferous trees. This means the species grows on other plants, specifically cone-bearing trees, using them for support but not taking nutrients from them (like say a parasite would). Epiphytes are just like plants that live on other plants but do not harm their host.
The main body of the lichen, called the thallus, is light greenish-gray to almost white, growing to lengths of 1-4 inches and spreading to widths of 2-8 inches.
The thread-like structures of the thallus are composed of hyphae, tiny tubes that intertwine to form a network, providing the lichen with its shape and structure, and absorbing water and nutrients from the surrounding environment.
The outer layer of the thallus is called the cortex. Unlike many other lichen, the cortex of the Smooth Horsehair Lichen is smooth. The cortex is a protective layer, shielding the lichen from harsh weather and preventing it from drying out.
Beneath the cortex lies the photobiont layer. Lichen are a composite organism, a symbiotic partnership between fungi and algae. In the case of the Smooth Horsehair Lichen, it forms a symbiotic relationship with green algae from the Trebouxia family as its photosynthetic partner. The algae uses sunlight to produce food sugars, and contributes some to the fungus. The fungus in this photobiont layer under the cortex provides a safe habitat, water, and minerals to the algae.
I was curious, how the algae which I think of as like pond or ocean-dwelling, and the fungus, for lack a better term, meet. How does Trebouxia reach like the branches of those tall coniferous trees where the Horsehair Lichen grows?
The most likely way is through wind dispersal, Trebouxia cell fragments carried by the wind. Another possibility is that animals, such as birds or insects, might inadvertently carry Trebouxia cells on their bodies or in their droppings. Rain can also help to disperse the cells, splashing them from one surface to another. Once a Trebouxia cell lands on a suitable surface, like the bark of a coniferous tree, it can potentially encounter a compatible fungal partner and start the process of forming a new lichen thallus.
Smooth Horsehair Lichen, employs both sexual and asexual reproduction strategies. The primary mode is sexual. It produces spores, which are analogous to the seeds of other plants. The lichen develops specialized structures called apothecia, that are quarter inch yellow-orange disc-shapes. Spores form within the apothecia, which are released, to be dispersed primarily by the wind, though also by animals, rain, and gravity. If a spore lands in a suitable location and encounters a compatible algae partner, it can germinate and develop into a new lichen.
The Smooth Horsehair Lichen, unlike many others in the lichen family lacks specialized asexual reproductive structures but it can still reproduce asexually through fragmentation. When small pieces of the lichen thallus break off, are dispersed again by wind, animals, water, or gravity, they can, if they land in a suitable environment, develop into new lichens.
This is uh, challenging because the fungus and algae partners both have to successfully establish in the new location. The fungal spores must find a compatible algae partner, while the fragmented thallus pieces must contain both partners in the right proportions. And of course they have to be dispersed to a suitable habitat with appropriate light, moisture, and nutrient conditions to survive and grow.
The Horsehair Lichen demonstrates specific adaptations to these reproductive complexities. Its pendulous growth form, because it hangs, aids in wind dispersal of both spores and fragments. And the lichen’s protective cortex allows it to tolerate a wide range of environmental conditions, which also increases its chances of successful establishment in new locations.
Lichen, like all living things, need energy and nutrients to survive. In other plant species photosynthesis provides energy and the roots uptake soil nutrients. In the case of the Smooth Horsehair Lichen, energy is contributed by its symbiotic algae partner and nutrients are absorbed from the atmosphere.
Rainwater, fog, and dust particles carry dissolved minerals and when these come into contact with the lichen’s thallus, they can be absorbed directly through its surface. The lichen’s cell walls contain specialized molecules that can bind to specific ions of essential elements like nitrogen, phosphorus, and potassium. This ion exchange, allows the lichen to actively take up these nutrients from the air.
But this direct absorption of nutrients from the atmosphere also makes lichens highly sensitive to air pollution. Pollutants can accumulate in the lichen’s thallus, potentially harming both the fungus and algae. Scientists often observe lichens as bioindicators of air quality.
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In the dream to breath, to drink, to eat, and in the dream to feel it everywhere, inside myself, outside myself, tasting fog and drinking dewdrops, the wind passing through me and is of me, in me. To be close to the world, to be so soft to it, to be each day so near to the mechanics of living. In the dream.
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Historically, found across the New England coast from Massachusetts to Maine, and north into Canada, today the Smooth Horsehair Lichen is found in only seven sites in the Canadian provinces of New Brunswick, Newfoundland, Nova Scotia, Prince Edward Island, and Quebec.
This is the North American Atlantic Maritime Ecozone characterized by its proximity to the ocean, a maritime climate with moderate temperatures and high humidity. Summers are temperate with high temperatures reaching the mid-70s, while winters dip into the teens. The region receives an annual rainfall of 50 inches on average.
In this exposed coastal environment, the lichen is found on the branches of coniferous trees, specifically the balsam fir. These are rugged coasts with rocky cliffs and dense forests of evergreens. The air is often misty and salty. The canopy provides shelter for a variety of birds, including warblers, thrushes, and woodpeckers some of which use the lichen as nesting material. In the forest understory, there are ferns, mosses, and wildflowers like bunchberry and starflower. Squirrel, chipmunk, black bear, moose and deer roam the forest floor.
In its native habitat, the Smooth Horsehair Lichen is a food source for small invertebrates, such as insects and mites. It provides a microhabitat for other organisms trapping moisture and organic matter, creating favorable conditions for other flora, like mosses and liverworts. And it plays a role in nutrient cycling. Because it accumulates airborne nutrients, when it eventually decomposes it slowly releases those nutrients back into the soil.
Historically, anthropogenic (meaning human-caused) habitat loss was the primary driver of the Smooth Horsehair Lichen’s decline. Human development and resource gathering, specifically decades of over-logging of its coniferous forest home have substantially reduced its available habitat and fractured its population.
Today, the looming threat is human induced climate change. Shifting humidity levels (including rain, dew, and fog), and more intense weather events pose risks. Research on related lichen species suggests that changes in temperature and moisture can drastically alter abundance. Warmer, wetter winters—predicted effects of climate change in the Canadian Maritimes—will lead to further population declines.
There is also preliminary scientific concern that air pollution is a contributing factor. Other lichen species in its family have shown high sensitivity to pollutants, particularly increased atmospheric nitrogen, declining in areas with poor air quality. This is because, as you’ll remember, the lichen directly absorbs elements from the air.
Four of the populations of Smooth Horsehair Lichen are found in protected Canadian National Parks. But the species itself is not otherwise legally protected in Canada or the US.
The Smooth Horsehair Lichen has been considered critically endangered on the IUCN Red List since 2021 and their population is currently in decline.
Our most recent counts estimate that less than 30 Smooth Horsehair Lichen remain in the wild.
Citations 19:53
Botanical Journal of the Linnean Society, Volume 194, Issue 4 – https://doi.org/10.1093/botlinnean/boaa050
The Global Fungal Red List – https://redlist.info/iucn/species_view/341524/
IUCN – https://www.iucnredlist.org/species/194660286/194678109
Northeastern Naturalist. Vol. 27, monograph 16 – https://doi.org/10.1656/045.027.m1601
Persoonia - Molecular Phylogeny and Evolution of Fungi, Volume 42 – https://doi.org/10.3767/persoonia.2019.42.04
US National Parks Service – https://www.nps.gov/articles/lichens-as-bioindicators.htm
US Fish and Wildlife Service – https://www.fws.gov/story/2023-12/lichen-what-fungus-it
Wikipedia – https://en.wikipedia.org/wiki/Bryoria
Music 21:27
Pledge 28:46
I honor the lifeforce of the Smooth Horsehair Lichen. I will carry its human name in my record. I am grateful to have shared time on our planet with this being. I lament the ways in which I and my species have harmed and diminished this species.
And so, in the name of the Smooth Horsehair Lichen I pledge to reduce my consumption. And my carbon footprint. And curb my wastefulness. I pledge to acknowledge and attempt to address the costs of my actions and inactions. And I pledge to resist the harm of plant or animal kin or their habitat, by individuals, corporations, and governments.
I pledge my song to the witness and memory of all life, to a broad celebration of biodiversity, and to the total liberation of all beings.
