North America Native Plant

Wart Lichen

Botanical name: Pyrenula macularis

USDA symbol: PYMA4

Habit: lichen

Native status: Native to North America  

Synonyms: Anthracothecium maculare Zahlbr. (ANMA16)   

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 small, dark, bumpy patches that look almost like tiny warts. Meet Pyrenula macularis, commonly known as wart lichen – a ...

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 small, dark, bumpy patches that look almost like tiny warts. Meet Pyrenula macularis, commonly known as wart lichen – a fascinating little organism that’s doing more for your garden ecosystem than you might realize!

What Exactly Is Wart Lichen?

First things first – wart lichen isn’t actually a plant at all! It’s a lichen, which is a unique partnership between a fungus and algae (or sometimes cyanobacteria) living together in perfect harmony. Think of it as nature’s original roommate situation, where both parties benefit from the arrangement. The fungus provides structure and protection, while the algae produces food through photosynthesis.

Wart lichen gets its name from its distinctive appearance – it forms small, dark, warty or bumpy patches on tree bark. These crusty growths might not win any beauty contests, but they’re actually quite remarkable when you know what to look for.

Where You’ll Find This Native Wonder

Pyrenula macularis is native to North America, particularly thriving in the eastern regions of the continent. You’ll typically spot this lichen making its home on the bark of deciduous trees in forests and wooded areas. It has a particular fondness for humid environments where it can soak up moisture from the air.

Is Wart Lichen Good for Your Garden?

Absolutely! While you can’t exactly plant wart lichen (more on that in a moment), having it show up naturally in your garden is actually a great sign. Here’s why:

  • Air quality indicator: Lichens are incredibly sensitive to air pollution, so their presence indicates clean, healthy air around your property
  • Ecosystem support: They provide food and shelter for tiny insects and other small creatures
  • Soil building: Over time, lichens help break down rock and bark, contributing to soil formation
  • Natural beauty: Once you appreciate their subtle charm, lichens add interesting texture and character to tree bark

How to Identify Wart Lichen

Spotting Pyrenula macularis is like becoming a nature detective! Here’s what to look for:

  • Location: Look on the bark of deciduous trees, especially in shaded or partially shaded areas
  • Appearance: Small, dark-colored patches that appear warty or bumpy
  • Texture: Crustose (crusty) and firmly attached to the bark surface
  • Size: Individual patches are typically quite small, often less than an inch across
  • Color: Usually dark gray to blackish

Can You Grow Wart Lichen?

Here’s where things get interesting – you can’t really plant or cultivate wart lichen in the traditional sense. Lichens are incredibly slow-growing and have very specific environmental requirements that are nearly impossible to replicate artificially. They need just the right combination of humidity, air quality, and substrate to establish themselves.

The good news? You don’t need to do anything special to encourage them! If your garden has the right conditions – clean air, appropriate trees, and adequate moisture – wart lichen may eventually show up on its own. This process can take years or even decades, so patience is key.

Creating Lichen-Friendly Conditions

While you can’t plant wart lichen directly, you can make your garden more hospitable to lichens in general:

  • Plant native trees: Deciduous trees native to your area provide the best substrate for local lichen species
  • Avoid chemical treatments: Skip the fungicides and other harsh chemicals that can harm these sensitive organisms
  • Maintain good air quality: Support local environmental initiatives that keep air pollution low
  • Create humid microclimates: Areas near water features or in partial shade tend to be more lichen-friendly

The Bottom Line

Wart lichen might not be the showiest addition to your garden, but it’s definitely one of the most beneficial. Think of it as nature’s seal of approval – when you spot these little crusty patches on your trees, you’ll know you’re maintaining a healthy, clean environment that supports biodiversity from the ground up (or should we say, from the bark out?).

So next time you’re wandering around your garden, take a moment to appreciate these tiny marvels. They may be small and unassuming, but they’re working hard to keep your local ecosystem healthy and thriving!

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 macularis (Zahlbr.) 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