Dot Lichen: The Tiny Garden Helper You Never Knew You Had
If you’ve ever taken a close look at the bark of trees in your garden, you might have noticed tiny dark spots scattered across the surface. Meet Arthonia arthonioides, commonly known as dot lichen – one of nature’s most understated yet beneficial organisms that’s probably already calling your landscape home.
What Exactly Is Dot Lichen?
Don’t let the name fool you – dot lichen isn’t actually a plant at all! It’s a fascinating partnership between a fungus and an algae (and sometimes a cyanobacterium too) living together in perfect harmony. This symbiotic relationship creates what we see as small, dark, dot-like patches on tree bark and occasionally on rocks.
Arthonia arthonioides is native to North America and has been quietly contributing to our ecosystems for centuries. You might also see it listed under its scientific synonym, Arthonia aspera, in older field guides.
Where You’ll Find Dot Lichen
This hardy little organism makes its home across North America, showing up wherever conditions are just right – which is more places than you might think! It’s particularly fond of the bark of deciduous trees and can occasionally be found on rocks in shaded areas.
Identifying Dot Lichen in Your Garden
Spotting dot lichen is like playing nature’s version of connect-the-dots. Here’s what to look for:
- Small, dark brown to black circular spots on tree bark
- Spots typically measure 1-3 millimeters across
- Flat appearance that seems almost painted onto the bark surface
- Usually found on smooth to moderately rough bark
- More abundant on the shaded sides of trees
Why Dot Lichen Is Actually Good News for Your Garden
Finding dot lichen in your landscape is like getting a green thumbs-up from Mother Nature herself. Here’s why you should be happy to see these tiny spots:
Air Quality Indicator: Lichens are incredibly sensitive to air pollution. Their presence means your garden enjoys relatively clean air – something both you and your plants can appreciate.
Ecosystem Support: While dot lichen doesn’t provide nectar like flowering plants, it does contribute to the micro-ecosystem of your garden. Some small insects use lichen for shelter and nesting material, and it’s part of the complex web of life that keeps gardens healthy.
No Harm to Trees: Unlike some organisms that grow on trees, dot lichen doesn’t harm its host. It simply uses the bark as a place to live while making its own food through photosynthesis.
How to Encourage Dot Lichen (Without Actually Planting It)
You can’t exactly pop down to the nursery and pick up a flat of dot lichen, but you can create conditions that welcome it:
- Maintain mature trees with interesting bark textures
- Avoid using harsh chemicals or pesticides that might affect air quality
- Keep some areas of your garden naturally shaded and humid
- Be patient – lichens grow very slowly and appear when conditions are right
Living With Your Lichen Neighbors
The best thing about dot lichen? It’s the ultimate low-maintenance garden resident. It asks for nothing, harms nothing, and quietly goes about its business of being a tiny but important part of your garden’s ecosystem.
If you spot these little dark dots on your trees, take a moment to appreciate them. They’re a sign that your garden is healthy, your air is clean, and you’re providing habitat for some of nature’s most resilient and fascinating partnerships. In the world of native gardening, sometimes the smallest residents make the biggest difference.
