North America Native Plant

Wart Lichen

Botanical name: Pyrenula martinicana

USDA symbol: PYMA7

Habit: lichen

Native status: Native to North America  

Synonyms: Parathelium martinicanum Vain. (PAMA22)   

Wart Lichen: The Tiny Garden Guardian You Didn’t Know You Had If you’ve ever taken a close look at the bark of trees in your garden and noticed small, dark, bumpy growths that look almost like tiny warts, you might have encountered Pyrenula martinicana, commonly known as wart lichen. Don’t ...

Wart Lichen: The Tiny Garden Guardian You Didn’t Know You Had

If you’ve ever taken a close look at the bark of trees in your garden and noticed small, dark, bumpy growths that look almost like tiny warts, you might have encountered Pyrenula martinicana, commonly known as wart lichen. Don’t worry – despite its somewhat off-putting name, this little organism is actually a fascinating and beneficial addition to any woodland or shade garden ecosystem.

What Exactly Is Wart Lichen?

Before we dive deeper, let’s clear up a common misconception: lichens aren’t plants at all! Wart lichen is actually a symbiotic organism made up of a fungus and algae working together in perfect harmony. The fungus provides structure and protection, while the algae produces food through photosynthesis. It’s like nature’s ultimate roommate situation – everyone benefits!

Pyrenula martinicana gets its wart nickname from its distinctive appearance. These lichens form small, dark, raised bumps on tree bark that can look remarkably similar to warts. But unlike actual warts, these little bumps are signs of a healthy, clean environment.

Where You’ll Find Wart Lichen

This native North American species thrives in the warm, humid climates of the southeastern United States and extends into Caribbean regions. You’re most likely to spot wart lichen in areas with clean air and adequate moisture – it’s particularly fond of hardwood trees in shaded woodland environments.

Is Wart Lichen Good for Your Garden?

Absolutely! Finding wart lichen in your garden is actually something to celebrate. Here’s why:

  • Air quality indicator: Lichens are extremely sensitive to air pollution, so their presence indicates clean, healthy air in your garden space
  • Ecosystem support: While they don’t directly attract pollinators like flowering plants, lichens provide food and habitat for various small insects and invertebrates
  • Authentic woodland character: They add natural texture and authenticity to shade gardens and woodland landscapes
  • Zero maintenance: Once established, they require absolutely no care from you

How to Identify Wart Lichen

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

  • Location: Look on the bark of hardwood trees, especially in shaded areas
  • Appearance: Small, dark brown to black, raised bumps that resemble tiny warts
  • Size: Individual growths are typically just a few millimeters across
  • Texture: Rough, warty surface that’s firmly attached to the bark
  • Pattern: Often appears in scattered patches rather than large colonies

Creating Conditions for Wart Lichen

While you can’t exactly plant wart lichen like you would a flower, you can create conditions that welcome it to your garden naturally:

  • Maintain clean air: Avoid using harsh chemicals or pesticides that could harm these sensitive organisms
  • Provide shade: Plant or preserve hardwood trees that create dappled shade conditions
  • Keep it humid: Ensure adequate moisture through natural rainfall or gentle watering of surrounding plants
  • Be patient: Lichens grow very slowly, so it may take years for them to establish naturally

The Bottom Line

Wart lichen might not be the showiest addition to your garden, but it’s certainly one of the most beneficial. Think of it as nature’s stamp of approval on your gardening practices. When you spot these tiny, warty growths on your trees, take a moment to appreciate the complex ecosystem thriving right in your backyard.

Rather than trying to remove or discourage wart lichen, embrace it as a sign that you’re creating a healthy, balanced environment for all kinds of life to flourish. After all, in the world of gardening, sometimes the smallest and most overlooked organisms can tell us the most about the health of our green spaces.

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 martinicana (Vain.) 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