Rim Lichen: A Fascinating Natural Occurrence in Your Landscape
If you’ve ever noticed crusty, grayish-white patches growing on rocks around your property, you might have encountered rim lichen (Lecanora deplanans). While this isn’t a plant you can pick up at your local nursery, understanding this fascinating organism can help you appreciate the complex ecosystem already thriving in your landscape.
What Exactly Is Rim Lichen?
Rim lichen is actually a remarkable partnership between a fungus and algae living together in what scientists call a symbiotic relationship. The fungus provides structure and protection, while the algae produces food through photosynthesis. Together, they create those distinctive crusty patches you see on rocks and stone surfaces.
Native to North America, rim lichen naturally occurs throughout western regions, particularly thriving on calcareous (limestone-rich) rocks and cliff faces. You’re most likely to spot it on exposed stone surfaces where it can access both sunlight and moisture.
How to Identify Rim Lichen
Rim lichen forms distinctive crusty patches that can help you identify it:
- Appears as grayish-white to pale yellow crusty growths
- Forms circular or irregular patches on rock surfaces
- Has a somewhat powdery or granular texture
- Typically found on limestone, concrete, or other calcium-rich surfaces
- May have slightly raised edges around the patches
Is Rim Lichen Beneficial in Your Garden?
While you can’t plant rim lichen like traditional garden plants, its presence can actually indicate a healthy environment. Here’s why rim lichen might be a welcome sight:
- Air quality indicator: Lichens are sensitive to air pollution, so their presence suggests good air quality in your area
- Natural beauty: These organisms add interesting texture and natural character to stone features
- Ecosystem support: Some small insects and arthropods may find shelter among lichen growths
- Soil building: Over very long periods, lichens help break down rock surfaces, contributing to soil formation
Understanding Lichen in Your Landscape
If you discover rim lichen growing on stone walls, boulders, or concrete surfaces in your garden, consider it a sign of a balanced natural environment. Unlike plants that you actively cultivate, lichens appear and thrive when conditions are just right.
Rim lichen prefers:
- Calcareous (limestone-rich) surfaces
- Areas with good air circulation
- Locations that receive some moisture but aren’t constantly wet
- Surfaces that get partial sunlight
Should You Encourage or Remove Rim Lichen?
Generally, there’s no need to actively encourage or discourage rim lichen. It won’t harm your hardscaping materials and can actually add natural character to stone features. However, if you prefer a cleaner look on your stone surfaces, gentle brushing when the lichen is dry can remove it, though it may eventually return if conditions remain favorable.
Remember that lichens grow extremely slowly, so what you’re seeing has likely been developing for years or even decades. Their presence connects your garden to the broader natural world, creating habitat for tiny creatures and contributing to the complex web of life that makes landscapes truly vibrant.
The Bottom Line
Rim lichen represents one of nature’s most successful partnerships, quietly going about its business on the rocks and stones in your landscape. While you can’t plant it like a traditional garden specimen, appreciating its presence can deepen your connection to the natural processes happening right in your own backyard. Next time you spot those crusty patches on stone surfaces, take a moment to marvel at this ancient and resilient form of life.
