North America Native Plant

Willey’s Dot Lichen

Botanical name: Arthonia willeyi

USDA symbol: ARWI2

Habit: lichen

Native status: Native to North America  

Willey’s Dot Lichen: A Tiny Marvel Living on Your Trees Ever noticed tiny, almost microscopic dots scattered across tree bark in your yard? You might be looking at Willey’s dot lichen (Arthonia willeyi), a fascinating organism that’s probably been quietly decorating your trees without you even realizing it! What Exactly ...

Willey’s Dot Lichen: A Tiny Marvel Living on Your Trees

Ever noticed tiny, almost microscopic dots scattered across tree bark in your yard? You might be looking at Willey’s dot lichen (Arthonia willeyi), a fascinating organism that’s probably been quietly decorating your trees without you even realizing it!

What Exactly Is Willey’s Dot Lichen?

Before we dive in, let’s clear up what we’re dealing with here. Arthonia willeyi isn’t a plant in the traditional sense – it’s actually a lichen. Think of lichens as nature’s ultimate roommate situation: they’re a partnership between fungi and algae (or sometimes cyanobacteria) that decided to team up and make life work together. The fungi provides the structure and protection, while the algae handles the food production through photosynthesis. It’s been working out pretty well for them for millions of years!

Willey’s dot lichen is what scientists call a crustose lichen, meaning it forms a crusty coating that’s tightly attached to its host surface – in this case, tree bark. As the name suggests, it appears as tiny dots or small patches, often so small you might miss them entirely unless you’re really looking.

Where You’ll Find This Tiny Tenant

This lichen is native to North America, though specific details about its exact range are still being studied by researchers. What we do know is that it’s one of those quiet natives that has been part of our ecosystems far longer than any of our cultivated garden plants.

Is Willey’s Dot Lichen Good for Your Garden?

Here’s the thing about lichens – they’re not something you plant, but rather something that finds you! And when they do show up, it’s actually fantastic news for your garden ecosystem. Here’s why:

  • Air quality indicators: Lichens are incredibly sensitive to air pollution, so their presence suggests your garden has relatively clean air
  • Biodiversity boosters: They provide food and habitat for tiny insects and other microorganisms
  • Zero maintenance: They take care of themselves completely – no watering, fertilizing, or pruning required
  • Harmless to trees: Despite living on bark, they don’t harm their host trees at all

How to Identify Willey’s Dot Lichen

Spotting Arthonia willeyi requires a bit of detective work and maybe a magnifying glass! Here’s what to look for:

  • Size: Very small, often just tiny dots or small patches
  • Color: Typically dark, ranging from blackish to dark brown
  • Location: Found on tree bark, particularly smooth-barked trees
  • Texture: Forms a thin, crusty layer that’s firmly attached to the bark
  • Shape: Appears as small, rounded dots or slightly irregular patches

The best time to spot lichens is when they’re slightly moist – after rain or in the early morning when there’s dew. They tend to be more visible and their colors more pronounced when hydrated.

Creating a Lichen-Friendly Garden

While you can’t plant Willey’s dot lichen, you can certainly create conditions that welcome lichens in general:

  • Minimize air pollution: Avoid excessive use of chemicals and support clean air initiatives
  • Maintain diverse tree species: Different lichens prefer different types of bark
  • Avoid pressure washing: Gentle cleaning methods protect existing lichen communities
  • Be patient: Lichens grow very slowly, so established communities are precious

The Bottom Line

Willey’s dot lichen might not be the showstopper centerpiece of your garden, but it’s a fascinating example of the complex, interconnected web of life that exists right in our backyards. These tiny organisms represent millions of years of evolutionary cooperation and serve as living indicators of environmental health.

So next time you’re in your garden, take a moment to examine your tree bark closely. You might just discover you’ve been hosting these remarkable little partnerships all along – and that’s something worth celebrating!

Willey’s Dot Lichen

Classification

Group

Lichen

Kingdom

Fungi - Fungi

Subkingdom
Superdivision
Division

Ascomycota - Sac fungi

Subdivision
Class

Ascomycetes

Subclass
Order

Arthoniales

Family

Arthoniaceae Rchb.

Genus

Arthonia Ach. - dot lichen

Species

Arthonia willeyi Tuck. - Willey's dot lichen

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