The
lichens have awoken.
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| Lichens, moss, and mushrooms in the Palisades. Photo by PBM. Used with permission. |
Late autumn, almost winter. The trees are bare and the sky is grey. A light mist falls. New York City seems devoid of life. Scaffolding drips and trains run late.
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| Grey day on the Hudson River. Photo by PBM. Used with permission. |
Across
the Hudson River, a few miles away from the dead-grey of the city in the
Palisades Interstate Park in New Jersey delicate greens and specks of mustard
yellow coat rocks and trees in a quietly vibrant layer.
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| Lichens on a rock in the Palisades. Photo by PBM. Used with Permission. |
On
a cheerful sunny day, the same lichen appear as a crusty dust on a rock, but in
the dismal rain these creatures burst forth.
My
rainy hike in the Palisades reminded me of my love for lichen and then I
realized something rather embarrassing: I knew relatively nothing about my
favorite organisms. The lichens I saw inspired me to learn more about them.
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| Lichens on a tree in the Palisades. Photo by PBM. Used with permission. |
Lichens
are intricate beings, and before we can delve into their complexities, let’s
start with the basics.
What Are Lichens?
Lichens
are the product of a mutually-beneficial relationship between fungi (the mycobiont)
and algae or cyanobacteria (the photobiont).
What
does this mean?
Basically,
a fungus and an algae or a cyanobacteria join forces for better living, and in
the process, they form what we call a lichen.
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| Lichens on a gravestone at Cortland Rural Cemetery. Photo by PBM. Used with permission. |
Not
all fungi and algae/cyanobacteria are well-suited for the lichen life. For fungi
which thrive in a lichen relationship, the process of selecting a worthy
photobiont is a ruthless one.
A
fungi will try to form a partnership with any nearby algae/cyanobacteria. As
the partnership is forming, the fungi try to kill off the algae/cyanobacteria. Any
algae/cyanobacteria that survives the attempted slaughter is deemed a suitable
partner by the fungi and the two will form a lichen together.
What do Lichens Look Like?
Internal Structure
In
primitive lichens, the cells of the mycobionts and photobionts are thrown together
in a miscellaneous mishmash, but more advanced lichens have distinct layers
with specific functions.
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| Lichen diagram by blog author. |
External Appearance
Lichens
are strange hybrids which look like neither fungi nor algae/cyanobacteria. There
are three main types of lichen:
fruticose lichens,
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| Fruticose lichen photo by Jason Hollinger. A creative commons image. Source. |
foliose lichens,
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| Foliose lichen photo by Norbert Nagel. A creative commons image. Source. |
and
crustose lichens.
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| Crustose lichen photo by Roger Griffith. A creative commons image. Source. |
Then,
there are countless variations on these basic types.
The
physical characteristics of lichens are influenced by lichen acids, byproducts
of lichen metabolism. These acids often give a lichen its characteristic color.
Lichens
in the sun look almost completely different than lichens on a rainy day. Why?
Lichens shrivel up and hibernate when the air is dry to reduce water loss, they
open up again to soak up water when the air is moist. Wet days are the best
days to observe lichens in all their glory.
Pollution
Lichens
absorb water indiscriminately without filtering it. This means they also absorb
all the pollutants in the water. Often these poisonous pollutants are too much
for the poor lichens to handle, which is why there aren’t many lichens in large
cities. The lichens that survive intense pollution tend to be small since their
already slow growth is stunted by pollution.
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| Lichen on a NYC street tree. Photo by blog author. |
Lichen Reproduction
Some
of the lichens I noticed on my hike were covered in dark dots. These dots are a
common type of spore-producing growth called disc-shaped apothecia produced by
the fungal partner of the lichen for sexual reproduction. Lichens produce spores
all year round, and like lichens themselves, the spore production sites are
mainly active when wet.
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| Lichens in the Palisades with spore-producing growths. Photo by PBM. Used with permission. |
The
odd thing about lichens is since they are a combination of two organisms, only
the fungal part of the lichen can reproduce sexually. The spores the fungi
release may grow as a pure fungus, they may die, or they may find a photobiont partner
and become lichens, possibly a different type of lichen then their parent.
Lichens
also reproduce asexually when small pieces of the mother organism break off and
are carried away animals, wind, or water to a new home. To speed along asexual reproduction,
lichens produce isidia—small outgrowths which break off easily—and soredia—powdery
granules of a few cells which can blow and float to a new location.
Lichen Longevity
Once
a lichen does set up shop, it can live for thousands of years. Lichens grow incredibly
slowly, so it is a good thing that they can live so long. One lichen in northern
Sweden is thought to be over 9,000 years old!
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| Lichens on a gravestone at Cortland Rural Cemetery. Photo by PBM. Used with permission. |
Now
that I’ve learned some lichen basics I hope to start identifying the species of
lichens I see. If you know what species any of the lichens in the photos from this
post are, please let me know in the comments!
