North America Native Plant

Barnacle Lichen

Botanical name: Thelotrema lathraeum

USDA symbol: THLA9

Habit: lichen

Native status: Native to North America  

Synonyms: Ocellularia lathraea (Tuck.) Zahlbr. (OCLA4)   

Barnacle Lichen: A Tiny Natural Wonder on Your Trees Have you ever noticed small, crusty patches with tiny holes dotting the bark of trees in your yard? You might be looking at barnacle lichen (Thelotrema lathraeum), a fascinating organism that’s neither plant nor animal, but something wonderfully unique in between! ...

Barnacle Lichen: A Tiny Natural Wonder on Your Trees

Have you ever noticed small, crusty patches with tiny holes dotting the bark of trees in your yard? You might be looking at barnacle lichen (Thelotrema lathraeum), a fascinating organism that’s neither plant nor animal, but something wonderfully unique in between!

What Exactly is Barnacle Lichen?

Barnacle lichen is actually a partnership between a fungus and algae working together in perfect harmony. This crustose lichen forms thin, grayish to whitish crusts on tree bark, decorated with distinctive tiny pores called ostioles that give it its barnacle appearance. These little crater-like openings are where the lichen releases its spores.

Scientifically known as Thelotrema lathraeum, this species was previously classified under the synonym Ocellularia lathraea. But don’t let the fancy names intimidate you – this is simply one of nature’s most successful collaborations!

Where You’ll Find Barnacle Lichen

This native North American lichen is most commonly found in the eastern and southeastern regions of the continent, thriving in humid, forested environments. It particularly loves the bark of mature hardwood trees in areas with clean air and adequate moisture.

Is Barnacle Lichen Good for Your Garden?

Absolutely! While you can’t plant or cultivate barnacle lichen like a traditional garden plant, its presence is actually a wonderful sign. Here’s why you should celebrate finding it:

  • It indicates good air quality – lichens are sensitive to pollution and only thrive in clean environments
  • It doesn’t harm trees – lichens are epiphytes that simply use bark as a surface to grow on
  • It adds subtle natural beauty and texture to tree bark
  • It contributes to the ecosystem by providing microscopic habitat

How to Identify Barnacle Lichen

Spotting barnacle lichen is like going on a tiny treasure hunt! Look for these key features:

  • Thin, crusty patches on tree bark that appear grayish-white to pale
  • Small, round pores or holes scattered across the surface
  • Smooth texture between the pores
  • Typically found on the bark of mature trees, especially in shaded areas
  • Size ranges from small patches to larger colonies covering several inches of bark

Creating Lichen-Friendly Conditions

While you can’t plant barnacle lichen, you can encourage its natural occurrence:

  • Maintain mature trees in your landscape
  • Avoid using harsh chemicals or pesticides near trees
  • Keep areas around trees relatively undisturbed
  • Ensure adequate moisture through natural or supplemental watering
  • Plant native trees that provide good lichen habitat

A Sign of a Healthy Ecosystem

Finding barnacle lichen in your yard is like receiving a gold star from nature! These sensitive organisms only establish themselves where air quality is good and conditions are just right. Rather than trying to remove them (please don’t!), consider them tiny badges of honor that show your landscape is supporting biodiversity.

So the next time you’re wandering around your yard, take a moment to look closely at your tree bark. You might just discover these amazing little partnerships quietly doing their part to make your outdoor space a richer, more vibrant ecosystem.

Barnacle Lichen

Classification

Group

Lichen

Kingdom

Fungi - Fungi

Subkingdom
Superdivision
Division

Ascomycota - Sac fungi

Subdivision
Class

Ascomycetes

Subclass
Order

Graphidales

Family

Thelotremataceae Stizenb.

Genus

Thelotrema Ach. - barnacle lichen

Species

Thelotrema lathraeum Tuck. - barnacle lichen

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