North America Native Plant

Protothelenella Lichen

Botanical name: Protothelenella corrosa

USDA symbol: PRCO

Habit: lichen

Native status: Native to North America  

Synonyms: Microglaena corrosa (Körb.) Arnold (MICO17)   

Protothelenella Lichen: A Tiny Garden Helper You Might Already Have Have you ever noticed tiny, crusty patches on rocks or tree bark in your garden and wondered what they were? You might be looking at a lichen – and possibly even the fascinating Protothelenella corrosa, commonly known as protothelenella lichen. ...

Protothelenella Lichen: A Tiny Garden Helper You Might Already Have

Have you ever noticed tiny, crusty patches on rocks or tree bark in your garden and wondered what they were? You might be looking at a lichen – and possibly even the fascinating Protothelenella corrosa, commonly known as protothelenella lichen. While this little organism might not be the showstopper you’d typically plant in your flower beds, it’s actually a remarkable native species that could already be quietly contributing to your garden’s ecosystem.

What Exactly Is Protothelenella Lichen?

Protothelenella corrosa is a type of crustose lichen native to North America. Now, before your eyes glaze over at the word crustose, let me explain this in simple terms. A crustose lichen is basically a flat, crusty organism that forms tight patches on surfaces like rocks, tree bark, or even concrete. Think of it as nature’s living paint that actually benefits the environment.

This particular lichen was previously known by the scientific name Microglaena corrosa, so you might see it referenced that way in older field guides or botanical texts.

Where You’ll Find This Little Wonder

As a North American native, protothelenella lichen has naturally established itself across various regions of the continent. However, specific distribution details for this particular species aren’t well-documented in popular gardening resources, which tells us something important: this is one of those quiet, behind-the-scenes players in nature’s orchestra.

Is It Beneficial to Have in Your Garden?

While you probably won’t be rushing to your local nursery to buy protothelenella lichen (spoiler alert: they don’t sell it), having it naturally appear in your garden is actually a good sign. Here’s why lichens like this one are garden gold:

  • They indicate good air quality – lichens are sensitive to pollution
  • They slowly break down rock and organic matter, contributing to soil formation
  • They provide habitat for tiny creatures that are part of the broader ecosystem
  • They add natural texture and interest to otherwise bare surfaces

How to Identify Protothelenella Lichen

Spotting this lichen requires a bit of detective work since it’s quite small and inconspicuous. The name corrosa actually gives us a clue – it means corroded or eroded, which describes the lichen’s somewhat weathered appearance.

Look for:

  • Small, crusty patches that seem to be painted onto rock or bark surfaces
  • A somewhat eroded or pitted texture
  • Colors that typically range from grayish to brownish (though this can vary)
  • Growth that follows the contours of whatever surface it’s on

Keep in mind that definitively identifying lichen species often requires microscopic examination, so if you’re curious about the exact species in your garden, you might want to contact a local botanist or mycologist.

Should You Encourage It in Your Garden?

The beautiful thing about native lichens like Protothelenella corrosa is that they don’t need your help – they’ll show up when conditions are right. If you want to create a lichen-friendly environment, focus on:

  • Maintaining good air quality around your property
  • Avoiding unnecessary use of chemicals that might affect sensitive organisms
  • Leaving some natural surfaces like rocks or older tree bark undisturbed
  • Being patient – lichens grow very slowly

The Bottom Line

While Protothelenella corrosa might not be the star of your garden show, it’s one of those unsung heroes that contributes to a healthy, functioning ecosystem. If you spot what you think might be this lichen in your garden, consider yourself lucky – you’re hosting a native species that’s been quietly doing its job for potentially decades.

Rather than trying to cultivate lichens (which is notoriously difficult), focus on creating the kind of healthy, chemical-free environment where native species like protothelenella lichen can thrive naturally. Your garden – and the tiny creatures that call it home – will thank you for it.

Protothelenella Lichen

Classification

Group

Lichen

Kingdom

Fungi - Fungi

Subkingdom
Superdivision
Division

Ascomycota - Sac fungi

Subdivision
Class

Ascomycetes

Subclass
Order
Family

Protothelenellaceae

Genus

Protothelenella Rasanen - protothelenella lichen

Species

Protothelenella corrosa (Körb.) H. Mayrh. & Poelt - protothelenella lichen

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