North America Native Plant

Rimmed Lichen

Botanical name: Aspicilia perradiata

USDA symbol: ASPE15

Habit: lichen

Native status: Native to North America  

Synonyms: Lecanora perradiata Nyl. (LEPE17)   

Discovering the Rimmed Lichen: Nature’s Crusty Garden Guest Have you ever noticed those peculiar, crusty patches growing on rocks in your garden and wondered what exactly they are? Meet the rimmed lichen (Aspicilia perradiata), one of nature’s most fascinating collaborative organisms that might already be calling your outdoor space home! ...

Discovering the Rimmed Lichen: Nature’s Crusty Garden Guest

Have you ever noticed those peculiar, crusty patches growing on rocks in your garden and wondered what exactly they are? Meet the rimmed lichen (Aspicilia perradiata), one of nature’s most fascinating collaborative organisms that might already be calling your outdoor space home!

What Exactly Is a Rimmed Lichen?

Here’s where things get really interesting: lichens aren’t actually plants at all! They’re incredible partnerships between fungi and algae (or sometimes cyanobacteria), working together in perfect harmony. The rimmed lichen gets its name from the distinctive raised edges that form around its circular, crusty patches. Think of it as nature’s way of creating living medallions on rock surfaces.

This particular species goes by the scientific name Aspicilia perradiata, though you might also see it referred to by its synonym, Lecanora perradiata. But don’t worry about memorizing the fancy names – rimmed lichen tells you everything you need to know about its most recognizable feature.

Where You’ll Find This Native Beauty

The rimmed lichen is a proud North American native, particularly at home in the western regions of the continent. It has a special fondness for arid and semi-arid landscapes, where it thrives in conditions that would leave most other organisms high and dry.

Spotting Rimmed Lichen in Your Garden

Identifying rimmed lichen is like a fun treasure hunt in your own backyard. Here’s what to look for:

  • Circular, crusty patches that look almost painted onto rock surfaces
  • Distinctive raised rims or borders around the edges
  • Gray to whitish coloration that can sometimes appear almost chalky
  • Preference for rocky surfaces, stone walls, or well-drained soil areas
  • Patches that seem to grow slowly outward from the center

Is Rimmed Lichen Beneficial for Your Garden?

Absolutely! While you can’t exactly plant or cultivate rimmed lichen (it does its own thing, thank you very much), having it around is actually a wonderful sign. Here’s why you should celebrate finding it:

  • Air quality indicator: Lichens are incredibly sensitive to air pollution, so their presence suggests you have clean, healthy air in your garden
  • Soil stabilization: They help prevent erosion on rocky surfaces and slopes
  • Ecosystem support: While they don’t attract pollinators like flowering plants, they contribute to the overall biodiversity of your outdoor space
  • Natural beauty: They add interesting texture and subtle color to rock features and stone walls

Living with Lichens

The best part about rimmed lichen? It’s the ultimate low-maintenance garden resident. It doesn’t need watering, fertilizing, or any care whatsoever. In fact, it’s best to simply leave it alone to do what it does best – slowly and steadily creating those beautiful crusty patterns on your rocks.

If you’re lucky enough to have rimmed lichen in your garden, consider yourself blessed with a living indicator of environmental health. These remarkable organisms have been around for millions of years, quietly going about their business of turning bare rock into something more beautiful and ecologically valuable.

So next time you’re wandering through your garden, take a moment to appreciate these unassuming but incredible organisms. They’re proof that some of nature’s most amazing partnerships happen right under our noses – or should we say, right on our rocks!

Rimmed Lichen

Classification

Group

Lichen

Kingdom

Fungi - Fungi

Subkingdom
Superdivision
Division

Ascomycota - Sac fungi

Subdivision
Class

Ascomycetes

Subclass
Order

Lecanorales

Family

Hymeneliaceae Körb.

Genus

Aspicilia A. Massal. - rimmed lichen

Species

Aspicilia perradiata (Nyl.) Hue - rimmed lichen

Plant data source: USDA, NRCS 2025. The PLANTS Database. https://plants.usda.gov,. 2/25/2025. National Plant Data Team, Greensboro, NC USA