Native Plants

Cracked Lichen

Acarospora albomarginata

USDA symbol: ACAL13

North America: native

Have you ever noticed small, circular patches with distinctive white edges growing on rocks in your garden or local hiking trails? Meet the cracked lichen (Acarospora albomarginata), a fascinating organism that’s been quietly creating natural art on stone surfaces across North America for centuries. Before we dive in, let’s clear ...

Cracked Lichen: The Tiny Natural Artist Decorating Your Garden Rocks

Have you ever noticed small, circular patches with distinctive white edges growing on rocks in your garden or local hiking trails? Meet the cracked lichen (Acarospora albomarginata), a fascinating organism that’s been quietly creating natural art on stone surfaces across North America for centuries.

What Exactly Is Cracked Lichen?

Before we dive in, let’s clear up a common misconception: lichens aren’t plants at all! They’re actually a remarkable partnership between fungi and algae (or sometimes cyanobacteria), working together in what scientists call a symbiotic relationship. The fungus provides structure and protection, while the algae photosynthesize to create food for both partners. Pretty cool teamwork, right?

Cracked lichen, scientifically known as Acarospora albomarginata, is native to North America and belongs to a group called crustose lichens. These are the flat, crusty types that seem painted directly onto rock surfaces – because in a way, they are!

Where You’ll Find Cracked Lichen

This hardy little organism calls western North America home, thriving in arid and semi-arid regions where many other organisms struggle to survive. You’ll typically spot it decorating rocks, boulders, and stone surfaces in natural areas.

Identifying Cracked Lichen

Spotting cracked lichen is like finding nature’s own medallions scattered across rock faces. Here’s what to look for:

  • Small, circular patches that appear glued to rock surfaces
  • Distinctive white or pale margins around darker centers
  • Crusty, flat appearance that follows the contours of the rock
  • Individual patches typically measure just a few millimeters to a couple centimeters across
  • Often found in groups, creating natural mosaic patterns on stone

Is Cracked Lichen Beneficial in Your Garden?

While you can’t exactly plant cracked lichen like you would a flower, its presence in your garden is actually a wonderful sign! Here’s why you should appreciate these tiny organisms:

  • Air quality indicators: Lichens are sensitive to air pollution, so their presence suggests clean air in your garden
  • Natural beauty: They add subtle, natural decoration to rock walls, stone paths, and boulder features
  • Ecosystem support: While not major wildlife attractors, they contribute to the overall biodiversity of your outdoor space
  • Soil building: Over very long periods, they help break down rock surfaces, contributing to soil formation

Encouraging Cracked Lichen in Your Landscape

You can’t plant cracked lichen from a nursery, but you can create conditions where it might naturally appear:

  • Include natural stone features like rock gardens, boulder arrangements, or stone walls
  • Maintain good air quality around your property
  • Avoid using harsh chemicals or pressure washing stone surfaces
  • Be patient – lichens grow extremely slowly and may take years to establish

Living with Lichens

If cracked lichen appears on your garden stones or rock features, consider yourself lucky! These slow-growing organisms are harmless to structures and add a touch of ancient, natural beauty to your landscape. They require no care, no watering, and no fertilizing – they’re the ultimate low-maintenance garden residents.

The next time you’re exploring your garden or hiking local trails, take a moment to appreciate these remarkable partnerships between fungi and algae. Cracked lichen reminds us that some of nature’s most beautiful and resilient creations come in the smallest packages, quietly decorating our world one tiny medallion at a time.

Acarospora albomarginata is also known as...

Often we refer to plants by their common names. When shopping for plants the scientific name is the best way to positively identify the plant species you desire. But some plants have more than one name! While it doesn't happen often, nurseries might display one name while you're searching for another. Acarospora albomarginata is also known as:

Thelocarpon albomarginatum | USDA symbol: THAL6

Why do some plants have more than one name? Over time plant species may be renamed for a few reasons:

  1. Botanists in different regions named the same plant without knowing it had already been classified.
  2. A species was reclassified after scientific advances in, for example, DNA analysis.
  3. Slight variations within a species are sometimes mistakenly identified as entirely new species.

Classification

Group: Lichen
Kingdom: Fungi - Fungi
Division: Ascomycota - Sac fungi
Class: Ascomycetes
Order: Lecanorales
Family: Acarosporaceae Zahlbr.
Genus: Acarospora A. Massal. - cracked lichen

Species: Acarospora albomarginata (Herre) Salisb. - cracked lichen

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