North America Native Plant

Wart Lichen

Botanical name: Pyrenula microtheca

USDA symbol: PYMI7

Habit: lichen

Native status: Native to North America  

Synonyms: Parathelium microcarpum Riddle (PAMI16)   

Wart Lichen: The Tiny Garden Helper You Never Knew You Had Have you ever noticed tiny, dark bumps on the bark of trees in your yard and wondered what they were? Meet the wart lichen (Pyrenula microtheca), a fascinating little organism that’s been quietly contributing to your garden’s ecosystem without ...

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

Have you ever noticed tiny, dark bumps on the bark of trees in your yard and wondered what they were? Meet the wart lichen (Pyrenula microtheca), a fascinating little organism that’s been quietly contributing to your garden’s ecosystem without you even knowing it!

What Exactly Is Wart Lichen?

Despite its somewhat unappetizing name, wart lichen isn’t actually a plant at all. It’s a lichen – a remarkable partnership between a fungus and algae working together as one organism. The wart part of its name comes from the small, dark, bump-like structures (called perithecia) that dot its surface, giving it a slightly warty appearance when viewed up close.

This native North American species goes by the scientific name Pyrenula microtheca, though you might occasionally see it referenced by its synonym, Parathelium microcarpum Riddle in older botanical literature.

Where You’ll Find Wart Lichen

Wart lichen is native to North America and is most commonly found in the eastern regions of the continent, particularly thriving in the humid conditions of the southeastern United States. It makes its home on the bark of hardwood trees, where it forms thin, crusty patches that blend seamlessly with the tree’s natural bark patterns.

Is Wart Lichen Beneficial for Your Garden?

While you can’t plant or cultivate wart lichen like traditional garden plants, its presence is actually a wonderful sign for your garden’s health! Here’s why you should appreciate these tiny organisms:

  • Air quality indicators: Lichens are sensitive to air pollution, so their presence indicates relatively clean air in your garden
  • Ecosystem support: They provide habitat and food sources for tiny insects and other microscopic creatures
  • Natural beauty: They add subtle texture and natural character to tree bark
  • No harm to trees: Unlike some organisms, lichens don’t damage or parasitize their host trees

How to Identify Wart Lichen

Spotting wart lichen takes a keen eye, but once you know what to look for, you’ll start noticing it everywhere:

  • Location: Look on the bark of hardwood trees, especially in areas with good air circulation
  • Appearance: Forms thin, crusty patches that are often grayish or brownish in color
  • Distinctive feature: Small, dark, round bumps (perithecia) scattered across the surface – these are the warts that give it its common name
  • Size: Individual patches are typically quite small, often just a few inches across
  • Texture: Crusty and tightly attached to the bark surface

Living Harmoniously with Wart Lichen

The best thing about wart lichen is that it requires absolutely no care from you! In fact, trying to remove it could potentially harm your trees. Instead, consider it a sign that your garden ecosystem is healthy and balanced.

If you’re interested in encouraging more lichens in your garden, focus on maintaining good air quality and avoiding excessive use of chemical treatments on your trees. Lichens thrive in clean, unpolluted environments, so organic gardening practices naturally support their growth.

The Bottom Line

While wart lichen might not be the showstopper flower that draws admiring glances from neighbors, it’s a valuable member of your garden’s ecosystem. These humble little organisms serve as both indicators of environmental health and contributors to biodiversity. So the next time you spot those tiny dark bumps on your tree bark, give them a little nod of appreciation – they’re working hard to keep your garden ecosystem in balance!

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 microtheca 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