Rimmed Navel Lichen: A Fascinating Rock-Dwelling Organism in Your Landscape
Have you ever noticed crusty, circular patches with raised edges growing on rocks in your garden or local hiking trails? You might be looking at rimmed navel lichen (Rhizoplaca marginalis), a fascinating organism that’s neither plant nor animal, but something entirely unique in the natural world.
What Exactly Is Rimmed Navel Lichen?
Rimmed navel lichen is a composite organism made up of a fungus and algae living together in a mutually beneficial relationship. This partnership creates those distinctive crusty, circular patches you see adhered to rock surfaces. The rimmed navel common name comes from its appearance – these lichens form round patches with raised, rim-like edges that can remind you of a shallow bowl or navel.
Also known by its scientific name Rhizoplaca marginalis (and formerly called Lecanora marginalis), this lichen is a native species throughout North America, making it a legitimate part of our natural heritage.
Where You’ll Find This Rocky Resident
Rimmed navel lichen has made its home across western North America, particularly thriving in the arid regions of the southwestern United States. You’ll typically spot it growing on exposed rock surfaces, especially in areas with plenty of sunshine and low moisture levels.
What Does It Look Like?
Identifying rimmed navel lichen is relatively straightforward once you know what to look for:
- Circular, crusty patches that can range from small coin-sized spots to larger patches several inches across
- Distinctive raised rim or border around the edge of each patch
- Gray to brownish coloration, sometimes with a slight yellowish tint
- Firmly attached to bare rock surfaces
- Dry, crusty texture that might crack or flake at the edges
Is Rimmed Navel Lichen Beneficial in Your Garden?
While you can’t exactly plant or cultivate rimmed navel lichen like you would a flowering perennial, its presence in your landscape can actually be quite beneficial:
- Natural beauty: These lichens add subtle texture and color to rock features, walls, and natural stone elements
- Ecosystem indicator: Healthy lichen populations often indicate good air quality in your area
- Minimal maintenance: They require absolutely no care, water, or fertilizer from you
- Habitat value: Some small insects and arthropods may use lichen patches for shelter
Should You Encourage or Discourage It?
The short answer is: let it be! Rimmed navel lichen is a harmless native organism that poses no threat to your garden plants or structures. Unlike some aggressive species, lichens grow extremely slowly and won’t overtake or damage anything in your landscape.
If you have natural rock features, stone walls, or decorative boulders in your garden, consider any lichen growth a bonus rather than a problem. These organisms are actually quite sensitive to environmental changes and pollution, so their presence suggests your garden has clean air and a healthy ecosystem.
Living Alongside Lichens
Since rimmed navel lichen can’t be planted or propagated like traditional garden plants, the best approach is simply to appreciate it when it appears naturally. If you’re creating rock gardens or incorporating natural stone elements in your landscape design, you might eventually see various lichens, including this species, colonizing the surfaces over time.
Remember that lichens grow incredibly slowly – sometimes taking years to establish visible patches – so patience is key. Avoid using harsh chemicals or pressure washing on stone surfaces where you’d like to see lichen growth, as these can prevent or destroy these delicate organisms.
The Bottom Line
Rimmed navel lichen might not be the showstopper you plant for instant curb appeal, but it’s a fascinating example of nature’s ingenuity right in your own backyard. These hardy little organisms represent millions of years of evolutionary partnership, turning bare rock into living art with their distinctive rimmed patterns. Next time you spot those crusty circular patches on rocks around your property, take a moment to appreciate these remarkable survivors that ask for nothing but give subtle beauty in return.
