North America Native Plant

Wart Lichen

Botanical name: Pyrenula subferruginea

USDA symbol: PYSU5

Habit: lichen

Native status: Native to North America  

Synonyms: Parathelium subferrugineum Malme (PASU12)   

Wart Lichen: The Tiny Garden Helper You Never Knew You Had If you’ve ever taken a close look at the bark of trees in your yard, you might have noticed some crusty, grayish patches that look almost like they’re part of the bark itself. Meet the wart lichen (Pyrenula subferruginea) ...

Wart Lichen: The Tiny Garden Helper You Never Knew You Had

If you’ve ever taken a close look at the bark of trees in your yard, you might have noticed some crusty, grayish patches that look almost like they’re part of the bark itself. Meet the wart lichen (Pyrenula subferruginea) – a fascinating little organism that’s probably been quietly living in your garden ecosystem without you even realizing it!

What Exactly Is Wart Lichen?

Here’s where things get interesting: wart lichen isn’t actually a plant at all! It’s a lichen, which is a remarkable partnership between a fungus and algae (or sometimes cyanobacteria) living together in perfect harmony. Think of it as nature’s original roommate situation – the fungus provides shelter and gathers water and minerals, while the algae handles the food production through photosynthesis.

The botanical name Pyrenula subferruginea might be a mouthful, but wart lichen gives you a pretty good idea of what to expect. This lichen forms thin, crusty patches on tree bark, dotted with tiny black bumps that contain its reproductive structures.

Where You’ll Find This Native Beauty

Wart lichen is native to North America and tends to call the eastern regions home, particularly thriving in temperate forest environments. You’re most likely to spot it in shaded areas where trees have had time to establish themselves and create the perfect microclimate.

Spotting Wart Lichen in Your Garden

Identifying wart lichen is like becoming a nature detective. Here’s what to look for:

  • Thin, crusty patches that seem to be embedded in tree bark
  • Grayish to brownish coloration that blends seamlessly with bark
  • Small black dots (perithecia) scattered across the surface – these are the warts that give it its common name
  • Smooth, almost leather-like texture
  • Typically found on the bark of mature deciduous trees

Is Wart Lichen Good for Your Garden?

Absolutely! While you can’t plant or cultivate wart lichen (it does its own thing, thank you very much), having it in your garden is actually a wonderful sign. Lichens are incredible environmental indicators – they’re like nature’s air quality monitors. The presence of lichens, including wart lichen, suggests that your garden has relatively clean air and a healthy ecosystem.

Wart lichen also plays several beneficial roles:

  • Helps create microhabitats for tiny insects and other small creatures
  • Contributes to the overall biodiversity of your garden ecosystem
  • Assists in nutrient cycling as it slowly breaks down over time
  • Indicates that your garden environment is stable and healthy

Living Alongside Wart Lichen

The beauty of wart lichen is that it requires absolutely zero maintenance from you. It can’t be planted, watered, fertilized, or pruned. It simply exists as part of the natural cycle of your garden, appearing on tree bark when conditions are right.

If you’re hoping to encourage lichens in your garden, the best approach is to:

  • Maintain healthy, mature trees that provide suitable bark surfaces
  • Avoid using harsh chemicals or pesticides that might harm these sensitive organisms
  • Keep some shaded, undisturbed areas in your landscape
  • Be patient – lichens grow very slowly and establish themselves over time

The Bottom Line

Wart lichen might not be the showiest addition to your garden, but it’s certainly one of the most interesting. This native North American lichen serves as both an indicator of environmental health and a quiet contributor to your garden’s ecosystem. You can’t plant it, but you can certainly appreciate it – and feel good knowing that its presence means your garden is providing a healthy home for all sorts of fascinating life forms.

So next time you’re wandering through your garden, take a moment to look closely at your tree bark. You might just discover that you’ve been hosting these remarkable little organisms all along!

Wart Lichen

Classification

Group

Lichen

Kingdom

Fungi - Fungi

Subkingdom
Superdivision
Division

Ascomycota - Sac fungi

Subdivision
Class

Ascomycetes

Subclass
Order

Pyrenulales

Family

Pyrenulaceae Rabenh.

Genus

Pyrenula Ach. - wart lichen

Species

Pyrenula subferruginea (Malme) R.C. Harris - wart lichen

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