North America Native Plant

Arthrosporum

Botanical name: Arthrosporum

USDA symbol: ARTHR7

Habit: lichen

Native status: Native to North America  

Arthrosporum: The Quiet Garden Helper You Never Knew You Had Have you ever noticed those subtle, crusty patches on rocks, concrete surfaces, or stone walls in your garden and wondered what they were? Meet Arthrosporum, a fascinating lichen that’s probably been quietly living in your outdoor spaces without you even ...

Arthrosporum: The Quiet Garden Helper You Never Knew You Had

Have you ever noticed those subtle, crusty patches on rocks, concrete surfaces, or stone walls in your garden and wondered what they were? Meet Arthrosporum, a fascinating lichen that’s probably been quietly living in your outdoor spaces without you even realizing it. While it might not be as flashy as your prize roses or as dramatic as your towering sunflowers, this unassuming organism plays a surprisingly important role in your garden ecosystem.

What Exactly Is Arthrosporum?

First things first – Arthrosporum isn’t actually a plant at all! It’s a lichen, which is essentially nature’s ultimate partnership between a fungus and an algae (or sometimes cyanobacteria). Think of it as the botanical world’s version of a buddy system, where two completely different organisms team up to create something neither could achieve alone.

This particular lichen forms thin, crusty patches that range from grayish to whitish in color. It’s what scientists call a crustose lichen, meaning it grows flat against surfaces like a living paint job. You’ll typically find Arthrosporum making itself at home on rocks, concrete walls, stone pathways, and other hard surfaces throughout North America.

Where You’ll Find This Hardy Survivor

Arthrosporum is native to North America and has adapted to life in temperate regions across the continent. It’s particularly fond of areas with clean air – which actually makes it a pretty good indicator of your local air quality!

Is Arthrosporum Beneficial for Your Garden?

While Arthrosporum won’t attract butterflies or produce beautiful blooms, it does offer some unique benefits to your garden space:

  • Air quality indicator: The presence of healthy lichens like Arthrosporum suggests you have good air quality in your area
  • Natural character: It adds an authentic, weathered look to stone features and hardscaping
  • Ecosystem support: Provides habitat for tiny invertebrates and contributes to the overall biodiversity of your garden
  • Erosion prevention: Helps stabilize surfaces and can slow down weathering of stone features

How to Identify Arthrosporum in Your Garden

Spotting Arthrosporum is easier than you might think once you know what to look for:

  • Appearance: Look for thin, crusty patches that appear almost painted onto surfaces
  • Color: Typically grayish, whitish, or sometimes with a slight greenish tint
  • Texture: Smooth to slightly rough, firmly attached to the surface
  • Location: On rocks, concrete, stone walls, or other hard, non-living surfaces
  • Growth pattern: Forms irregular patches that may merge with neighboring colonies

Living Harmoniously with Your Lichen Neighbors

The beauty of Arthrosporum is that it requires absolutely no care from you – in fact, it prefers to be left alone! Here’s how to be a good neighbor to these quiet garden residents:

  • Don’t scrub it away: Resist the urge to power wash or scrub lichen off your stone features
  • Avoid harsh chemicals: Skip the bleach and harsh cleaners near areas where lichens grow
  • Embrace the patina: Think of lichen growth as nature’s way of aging your hardscaping beautifully
  • Maintain clean air: Support local air quality initiatives – your lichens will thank you

The Bottom Line

While you can’t exactly plant Arthrosporum in your garden (it’ll show up on its own if conditions are right), you can certainly appreciate and protect it when it does appear. This humble lichen is like having a built-in air quality monitor that doubles as natural garden art. Rather than seeing those crusty patches as something to scrub away, consider them a sign that your garden is part of a healthy, thriving ecosystem.

So the next time you’re strolling through your garden and spot those quiet, unassuming patches on your stone walls or rock features, give a little nod of appreciation to your Arthrosporum neighbors. They may not be the stars of your garden show, but they’re definitely valuable members of the supporting cast!

Arthrosporum

Classification

Group

Lichen

Kingdom

Fungi - Fungi

Subkingdom
Superdivision
Division

Ascomycota - Sac fungi

Subdivision
Class

Ascomycetes

Subclass
Order

Lecanorales

Family

Catillariaceae Hafellner

Genus

Arthrosporum A. Massal.

Species

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