Arthopyrenia degelii: The Mysterious Dark Crust Lichen in Your Backyard
If you’ve ever noticed dark, crusty patches on rocks or tree bark in your garden and wondered what they were, you might have encountered Arthopyrenia degelii. This fascinating little organism isn’t a plant at all—it’s actually a lichen, one of nature’s most intriguing partnerships between fungi and algae.
What Exactly Is Arthopyrenia degelii?
Arthopyrenia degelii is a crustose lichen, which means it forms a thin, crust-like layer that’s tightly attached to its substrate. Think of it as nature’s living paint job on rocks and bark. Unlike the plants we typically cultivate in our gardens, lichens are composite organisms made up of a fungus and an alga (or sometimes cyanobacteria) working together in a mutually beneficial relationship.
This particular lichen is native to North America and can be found naturally occurring in various regions across the continent, particularly in northeastern areas. It’s part of the incredible diversity of native species that contribute to healthy ecosystems.
How to Identify This Curious Lichen
Spotting Arthopyrenia degelii requires looking closely at the surfaces where it grows. Here’s what to look for:
- Dark, thin crusts that appear almost painted onto rock surfaces or tree bark
- Smooth to slightly rough texture
- Tightly adhered to the substrate (you can’t peel it off like you might with some other lichens)
- Often found in patches rather than covering entire surfaces
Is It Beneficial to Your Garden?
While Arthopyrenia degelii won’t add colorful blooms or attract butterflies like traditional garden plants, it does play some valuable ecological roles:
- Contributes to biodiversity in your outdoor spaces
- Helps break down rock surfaces very slowly, contributing to soil formation over geological time
- Serves as an indicator of air quality (lichens are sensitive to pollution)
- Provides microhabitat for tiny invertebrates
Should You Encourage or Discourage It?
The short answer is: just let it be! Arthopyrenia degelii isn’t something you can plant or remove easily, nor should you want to. As a native species, it’s doing its part in the local ecosystem. If you find it growing on rocks in your garden or on tree bark, consider it a sign that your outdoor space is supporting native biodiversity.
You can’t really grow lichens in the traditional sense—they appear naturally when conditions are right. They’re incredibly slow-growing and can take years or even decades to establish, so any lichen you see has likely been there for quite some time.
Creating Lichen-Friendly Spaces
If you’re interested in supporting native lichens like Arthopyrenia degelii in your landscape, here are some gentle approaches:
- Avoid using chemical treatments on rocks, walls, or tree trunks
- Maintain good air quality around your property
- Leave natural rock surfaces and older trees undisturbed when possible
- Reduce artificial lighting, which can sometimes interfere with lichen growth
The Bottom Line
Arthopyrenia degelii might not be the showstopper that a native wildflower meadow or butterfly garden would be, but it represents the often-overlooked complexity of native ecosystems. These quiet, persistent organisms have been around far longer than most other life forms, and they’ll likely continue their slow, steady work long after we’re gone.
Next time you’re wandering around your garden or local natural areas, take a moment to appreciate these dark crusty patches. They’re not just random stains on rocks—they’re living communities that have found their own unique way to thrive in the world around us.
