Arthothelium Lichen: The Quiet Guardian of Your Garden Trees
Have you ever noticed thin, grayish patches on the bark of your mature trees and wondered what they might be? You could be looking at arthothelium lichen (Arthothelium interveniens), a fascinating organism that’s actually doing your garden a favor just by being there!
What Exactly Is Arthothelium Lichen?
First things first – arthothelium lichen isn’t a plant at all. It’s actually a remarkable partnership between a fungus and algae working together as one organism. This collaboration creates what we see as thin, crusty patches on tree bark that might look unremarkable at first glance, but are actually quite extraordinary.
Arthothelium interveniens is native to North America and naturally occurs throughout eastern and central regions of the continent. You’ll typically find it making its home on the bark of deciduous trees in woodland areas.
How to Identify Arthothelium Lichen
Spotting this lichen is easier once you know what to look for:
- Forms thin, grayish-white to pale gray crusts directly on tree bark
- Has a smooth to slightly rough texture
- Features small, dark fruiting bodies (called apothecia) that look like tiny black dots scattered across the surface
- Grows flush against the bark surface rather than projecting outward
- Typically found on mature deciduous trees
Is It Beneficial to Have in Your Garden?
Absolutely! While you can’t plant or cultivate arthothelium lichen (more on that in a moment), having it naturally appear in your garden is actually a wonderful sign. Here’s why you should celebrate finding it:
- Air quality indicator: Lichens are incredibly sensitive to air pollution, so their presence indicates you have clean, healthy air in your garden
- Ecosystem health: They’re part of a healthy woodland ecosystem and indicate your garden environment is supporting native biodiversity
- Natural character: They add authentic woodland character to mature trees without causing any harm
- Wildlife habitat: While small, they can provide microhabitat for tiny insects and other small creatures
The Reality About Growing Lichens
Here’s something that might surprise you: you can’t actually plant, grow, or cultivate arthothelium lichen in your garden. Lichens have incredibly specific requirements and grow at their own pace in response to environmental conditions that are largely beyond our control.
What you can do is create conditions that might encourage lichens to establish naturally:
- Maintain mature trees, especially native deciduous species
- Avoid using chemical treatments on tree bark
- Keep air quality clean by avoiding excessive use of pesticides or other chemicals
- Be patient – lichens grow incredibly slowly and may take years to establish
Should You Be Concerned?
Not at all! A common misconception is that lichens growing on trees indicate the tree is unhealthy or dying. This simply isn’t true. Arthothelium lichen and other bark-dwelling lichens are harmless to trees – they’re just using the bark as a surface to live on, not feeding off the tree itself.
If you notice lichens on your trees, it’s actually a good sign that you’re providing a healthy environment for a diverse range of organisms.
The Bottom Line
While you can’t add arthothelium lichen to your shopping list at the garden center, discovering it naturally occurring on your trees is like receiving a certificate of environmental approval for your garden. These quiet, unassuming organisms are indicators of the health and quality of your outdoor space.
So next time you’re walking through your garden and spot those grayish crusts on your tree bark, take a moment to appreciate these remarkable partnerships between fungi and algae that have been thriving in North American forests for countless years. Your garden is clearly doing something right!
