Rim Lichen: The Crusty Garden Guest You Never Invited (But Should Appreciate)
Have you ever noticed pale, crusty patches growing on rocks, concrete walls, or even old tombstones in your yard? Meet rim lichen (Lecanora expallens) – a fascinating organism that’s probably been quietly decorating your landscape without you even realizing it!
What Exactly Is Rim Lichen?
Before we dive deeper, let’s clear up what rim lichen actually is – because it’s not quite what you might expect. Lecanora expallens isn’t a plant in the traditional sense. It’s a lichen, which is essentially a partnership between a fungus and an alga working together in perfect harmony. Think of it as nature’s ultimate roommate situation that actually works out!
This species is native to North America and goes by the scientific name Lecanora expallens, though you might also see it referenced by its synonym Lecanora conizaea in older field guides.
Where You’ll Spot This Crusty Character
Rim lichen has made itself at home across North America, showing up wherever there are suitable rocky surfaces and clean air to breathe. You’ll typically find it growing on:
- Limestone and other calcareous rocks
- Concrete structures like walls and sidewalks
- Weathered stone surfaces
- Sometimes on old wooden structures
How to Identify Rim Lichen
Spotting rim lichen is easier than you might think once you know what to look for. This crusty customer typically appears as:
- Grayish-white to pale yellow patches
- Crusty, almost scaly texture that looks like it’s been painted on
- Flat growth pattern that seems to merge with the rock surface
- Circular to irregular shaped colonies
- Small, dark dots (reproductive structures) scattered across the surface
Is Rim Lichen Beneficial for Your Garden?
While you can’t exactly plant rim lichen like you would a rose bush, its presence in your landscape is actually a wonderful sign! Here’s why you should appreciate this unassuming organism:
Air Quality Indicator: Lichens are incredibly sensitive to air pollution, so finding rim lichen thriving in your area means you’re breathing cleaner air. It’s like having a natural air quality monitor right in your backyard!
Ecosystem Support: While rim lichen doesn’t attract pollinators like flowering plants do, it plays its own important role in the ecosystem. Some small insects and other tiny creatures use lichens as habitat and food sources.
Natural Beauty: There’s something quietly beautiful about the way rim lichen decorates stone surfaces with its subtle patterns and colors. It adds character and a sense of age to garden walls and rock features.
Living with Rim Lichen
The wonderful thing about rim lichen is that it requires absolutely no care from you. In fact, trying to help it usually does more harm than good. This self-sufficient organism will:
- Colonize suitable surfaces naturally
- Grow extremely slowly (we’re talking decades for noticeable changes)
- Thrive in clean air conditions
- Persist through various weather conditions
If you’re lucky enough to have rim lichen growing on stone features in your garden, simply let it be. Avoid using harsh chemicals or pressure washing these surfaces, as lichens are quite delicate despite their crusty appearance.
The Bottom Line
While you can’t run out and buy rim lichen at your local nursery, discovering it growing naturally in your landscape is something to celebrate. It’s a sign of good air quality and adds a touch of natural patina to stone surfaces that money can’t buy. So next time you spot those crusty gray patches on your garden stones, give them a nod of appreciation – they’re working hard to make your little corner of the world a bit more interesting!
