North America Native Plant

Crenulate Rim Lichen

Botanical name: Lecanora crenulata

USDA symbol: LECR2

Habit: lichen

Native status: Native to North America  

Crenulate Rim Lichen: A Fascinating Natural Garden Guest Have you ever noticed those grayish, crusty patches growing on rocks or tree bark in your garden and wondered what they were? If they have distinctively scalloped edges, you might be looking at the crenulate rim lichen (Lecanora crenulata), a remarkable organism ...

Crenulate Rim Lichen: A Fascinating Natural Garden Guest

Have you ever noticed those grayish, crusty patches growing on rocks or tree bark in your garden and wondered what they were? If they have distinctively scalloped edges, you might be looking at the crenulate rim lichen (Lecanora crenulata), a remarkable organism that’s neither plant nor animal, but something wonderfully unique!

What Exactly Is Crenulate Rim Lichen?

Lichens are fascinating partnerships between fungi and algae (or sometimes cyanobacteria) that work together to create something entirely new. The crenulate rim lichen gets its name from its distinctive crenulate edges – think of the scalloped border on a pie crust, but in miniature. These gray-green crusty patches might look simple, but they’re actually complex living communities doing important work in your landscape.

Where You’ll Find This Native Beauty

Lecanora crenulata is native to North America and can be found across much of the continent. This hardy lichen makes itself at home in various environments, from urban parks to wild forests, always choosing spots where the air is reasonably clean.

Identifying Crenulate Rim Lichen

Spotting this lichen is like solving a gentle nature puzzle. Here’s what to look for:

  • Gray-green to pale gray crusty appearance
  • Distinctive scalloped or wavy edges (the crenulate part)
  • Typically found growing on rocks, tree bark, or other hard surfaces
  • Forms circular or irregular patches that can merge with neighboring colonies
  • Thin, closely attached to its substrate

Is It Beneficial for Your Garden?

Absolutely! While you can’t plant or cultivate crenulate rim lichen like traditional garden plants, its presence is actually a wonderful sign. Think of lichens as nature’s air quality monitors – they’re sensitive to pollution, so finding them in your garden suggests you have relatively clean air. Pretty cool, right?

Beyond being environmental indicators, lichens like Lecanora crenulata contribute to your garden’s ecosystem in subtle but important ways:

  • They slowly break down rock surfaces, contributing to soil formation over time
  • They add authentic natural character to rock gardens and naturalistic landscapes
  • They provide habitat for tiny insects and other microscopic creatures
  • They help stabilize surfaces and prevent erosion

Creating Lichen-Friendly Conditions

While you can’t plant lichens, you can definitely encourage them! If you’d like to see more of these fascinating organisms in your garden, consider these approaches:

  • Maintain good air quality by avoiding excessive use of chemicals
  • Leave some natural rock surfaces and mature tree bark undisturbed
  • Be patient – lichens grow very slowly, sometimes just millimeters per year
  • Avoid power washing or scrubbing areas where lichens are establishing

The Bottom Line

Crenulate rim lichen isn’t something you’ll find at the garden center, but discovering it growing naturally in your landscape is like finding a small treasure. These remarkable organisms remind us that some of the most interesting garden residents are the ones that choose us, rather than the ones we choose. Next time you spot those scalloped gray-green patches, take a moment to appreciate the complex partnership at work and the clean air it represents in your little corner of the world.

Remember, the presence of lichens like Lecanora crenulata is generally a positive sign for your garden’s health and environmental quality. So embrace these unexpected guests – they’re proof that your outdoor space is supporting diverse forms of life!

Crenulate Rim Lichen

Classification

Group

Lichen

Kingdom

Fungi - Fungi

Subkingdom
Superdivision
Division

Ascomycota - Sac fungi

Subdivision
Class

Ascomycetes

Subclass
Order

Lecanorales

Family

Lecanoraceae Körb.

Genus

Lecanora Ach. - rim lichen

Species

Lecanora crenulata Hook. - crenulate rim lichen

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