North America Native Plant

American Strigula Lichen

Botanical name: Strigula americana

USDA symbol: STAM9

Habit: lichen

Native status: Native to North America  

Synonyms: Arthopyrenia tenuis R.C. Harris (ARTE13)   

American Strigula Lichen: A Tiny Guardian of Your Garden’s Health Have you ever noticed small, dark patches on the bark of trees in your garden and wondered what they might be? You might be looking at American strigula lichen (Strigula americana), a fascinating little organism that’s actually doing your garden ...

American Strigula Lichen: A Tiny Guardian of Your Garden’s Health

Have you ever noticed small, dark patches on the bark of trees in your garden and wondered what they might be? You might be looking at American strigula lichen (Strigula americana), a fascinating little organism that’s actually doing your garden a big favor. While many gardeners focus on showy flowers and lush foliage, these humble lichens are quietly working as natural air quality monitors right in your backyard.

What Exactly Is American Strigula Lichen?

Let’s clear up a common misconception first: lichens aren’t plants at all! American strigula lichen is actually a partnership between a fungus and an algae, working together in perfect harmony. This particular species forms what scientists call a crustose lichen, meaning it grows as a thin, crusty layer that’s tightly attached to tree bark.

You might also see this species referred to by its scientific synonym, Arthopyrenia tenuis, but Strigula americana is the accepted name. It’s a native species to North America, making it a natural and beneficial part of our local ecosystems.

Where You’ll Find This Tiny Marvel

American strigula lichen calls eastern North America home, thriving in humid temperate regions where the air is clean and moisture levels are just right. It has a particular fondness for the smooth bark of deciduous trees, where it forms small, dark patches that might measure just a few millimeters across.

What Does It Look Like?

Identifying American strigula lichen takes a keen eye, as it’s quite small and unassuming. Here’s what to look for:

  • Thin, dark patches on smooth tree bark
  • Crusty, flat appearance that seems painted onto the bark
  • Very small size – individual patches are typically just a few millimeters
  • Dark brown to blackish coloration
  • Smooth texture without any leafy or branching structures

Is It Good for Your Garden?

Absolutely! While American strigula lichen won’t add colorful blooms to your landscape, its presence is actually a wonderful sign. Lichens are incredibly sensitive to air pollution, so finding them in your garden means you have good air quality. Think of them as nature’s own environmental monitoring system.

Here’s why you should appreciate these little organisms:

  • They indicate healthy, unpolluted air in your garden
  • They don’t harm trees – they’re just using the bark as a surface to grow on
  • They contribute to biodiversity in your woodland garden or naturalistic landscape
  • They’re part of the natural ecosystem that mature trees support

Can You Grow American Strigula Lichen?

Here’s where things get interesting – you can’t actually plant or cultivate lichens like you would traditional garden plants. American strigula lichen will establish itself naturally when conditions are right. You can’t buy seeds or seedlings at the garden center, and there’s no special planting technique to learn.

Instead, if you want to encourage lichens in your garden, focus on creating the right environment:

  • Maintain mature deciduous trees with smooth bark
  • Avoid using pesticides or fungicides that might harm these sensitive organisms
  • Keep air quality good by avoiding activities that create pollution
  • Maintain adequate humidity around your trees

The Best Gardens for American Strigula Lichen

This lichen thrives in woodland gardens and naturalistic landscapes where mature trees are the stars of the show. If you’re cultivating a forest-like environment or have established deciduous trees on your property, you’re already providing the perfect habitat.

It’s particularly well-suited for:

  • Woodland gardens with native trees
  • Mature landscapes with established canopy trees
  • Natural areas left relatively undisturbed
  • Gardens focused on supporting native biodiversity

A Sign of Garden Health

The next time you’re strolling through your garden and spot those tiny dark patches on your tree bark, take a moment to appreciate what you’re seeing. American strigula lichen might be small and easily overlooked, but its presence tells a bigger story about the health and quality of your garden environment. In a world where we’re increasingly concerned about air quality and environmental health, these little lichens serve as reassuring indicators that your outdoor space is thriving naturally.

Remember, you don’t need to plant, water, or tend to these remarkable organisms – they’re already hard at work, quietly contributing to your garden’s ecosystem while serving as tiny guardians of environmental quality.

American Strigula Lichen

Classification

Group

Lichen

Kingdom

Fungi - Fungi

Subkingdom
Superdivision
Division

Ascomycota - Sac fungi

Subdivision
Class

Ascomycetes

Subclass
Order

Sphaeriales

Family

Strigulaceae A.B. Frank

Genus

Strigula Fr. - strigula lichen

Species

Strigula americana R.C. Harris - American strigula lichen

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