North America Native Plant

Pore Lichen

Botanical name: Pertusaria rhexostoma

USDA symbol: PERH4

Habit: lichen

Native status: Native to North America  

Synonyms: Pertusaria finkii Zahlbr. ex Fink (PEFI4)   

Pore Lichen: A Fascinating Natural Garden Guest Have you ever noticed those crusty, grayish patches growing on the bark of your mature trees? You might be looking at pore lichen (Pertusaria rhexostoma), a fascinating organism that’s actually doing your garden a favor just by being there! What Exactly Is Pore ...

Pore Lichen: A Fascinating Natural Garden Guest

Have you ever noticed those crusty, grayish patches growing on the bark of your mature trees? You might be looking at pore lichen (Pertusaria rhexostoma), a fascinating organism that’s actually doing your garden a favor just by being there!

What Exactly Is Pore Lichen?

Despite its name suggesting it’s a plant, pore lichen is actually a remarkable partnership between a fungus and algae living together in perfect harmony. This collaboration creates those distinctive crusty patches you see on tree bark, and it’s been happening successfully for millions of years.

Pore lichen gets its common name from the tiny pores or holes (called ostioles) that dot its surface. These aren’t just decorative features – they’re actually the lichen’s way of releasing spores for reproduction.

Where You’ll Find This Native Beauty

Pertusaria rhexostoma is native to North America, with its primary range spanning the eastern regions of the continent. You’re most likely to spot it in the northeastern United States and southeastern Canada, where it has been quietly going about its business on tree bark for centuries.

How to Spot Pore Lichen in Your Garden

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

  • Crusty, pale gray to whitish patches on tree bark
  • Distinctive small pores or holes scattered across the surface
  • Typically found on the bark of mature deciduous trees
  • Patches can range from small spots to larger, merged colonies
  • Texture that’s rough and crusty rather than smooth or leafy

Is Pore Lichen Beneficial for Your Garden?

Absolutely! Having pore lichen in your garden is actually a wonderful sign. Here’s why you should be thrilled to see it:

  • Air quality indicator: Lichens are incredibly sensitive to air pollution, so their presence means your garden enjoys clean, healthy air
  • Completely harmless: Unlike some organisms that grow on trees, lichens don’t harm their host trees at all – they’re just along for the ride
  • Natural character: They add authentic, wild beauty to mature landscapes and woodland gardens
  • Low maintenance: They require absolutely no care from you – nature handles everything

Can You Plant Pore Lichen?

Here’s where pore lichen differs dramatically from traditional garden plants – you can’t actually plant it! This lichen appears naturally when conditions are just right. It needs:

  • Clean, unpolluted air
  • Moderate to high humidity levels
  • Suitable host trees (usually mature deciduous species)
  • Time – lichens grow very slowly

The best thing you can do to encourage lichen diversity in your garden is to maintain mature trees, avoid using harsh chemicals, and let nature take its course.

Living Alongside Your Lichen Guests

If you’re lucky enough to have pore lichen in your garden, simply enjoy it! There’s no maintenance required, no watering schedule to follow, and no pruning needed. Just appreciate these amazing organisms as living proof that your garden provides a healthy environment.

Remember, seeing lichens like Pertusaria rhexostoma on your trees is a badge of honor – it means you’re doing something right in creating a natural, unpolluted space where these sensitive organisms can thrive.

Pore Lichen

Classification

Group

Lichen

Kingdom

Fungi - Fungi

Subkingdom
Superdivision
Division

Ascomycota - Sac fungi

Subdivision
Class

Ascomycetes

Subclass
Order

Lecanorales

Family

Pertusariaceae Körb.

Genus

Pertusaria DC. - pore lichen

Species

Pertusaria rhexostoma Nyl. - pore lichen

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