Wart Lichen: The Unsung Hero Growing on Your Garden Walls
Have you ever noticed those grayish, bumpy patches on your stone walls, concrete planters, or brick pathways and wondered what they are? Meet the wart lichen (Verrucaria muralis), a fascinating organism that’s probably been quietly living in your garden all along. While it might not be the showiest addition to your landscape, this hardy little survivor has some surprising benefits worth knowing about.
What Exactly Is Wart Lichen?
First things first – wart lichen isn’t actually a plant at all! It’s a lichen, which is a unique partnership between a fungus and algae working together as one organism. Think of it as nature’s ultimate roommate situation, where both parties benefit from the arrangement. The fungus provides structure and protection, while the algae produces food through photosynthesis.
Verrucaria muralis gets its common name from its distinctive warty appearance. It forms thin, crusty patches that look like they’ve been painted onto stone surfaces, complete with tiny raised bumps that house the lichen’s reproductive structures.
Where You’ll Find This Hardy Survivor
Wart lichen is native to North America but has spread globally, making itself at home wherever there are suitable stone surfaces. You’ll typically spot it growing on:
- Concrete walls and foundations
- Stone retaining walls
- Brick pathways and patios
- Rock gardens and natural stone features
- Mortar joints between stones
This lichen has a particular fondness for calcareous (lime-rich) substrates, which is why it thrives on concrete and mortar – materials that contain limestone.
Identifying Wart Lichen in Your Garden
Spotting wart lichen is easier than you might think once you know what to look for:
- Color: Ranges from pale gray to dark grayish-black, sometimes with a slightly greenish tint when moist
- Texture: Forms a thin, crusty coating that feels rough to the touch
- Surface: Covered with small, wart-like bumps (perithecia) that contain spores
- Pattern: Often appears as irregular patches that can merge together over time
- Location: Almost exclusively found on hard surfaces like stone, concrete, and brick
Is Wart Lichen Beneficial to Your Garden?
While wart lichen won’t add vibrant blooms to your landscape, it does provide some subtle benefits:
Ecosystem Services: Like all lichens, wart lichen contributes to the breakdown of rock surfaces through a process called bioweathering. Over very long periods, this helps create soil and contributes to nutrient cycling.
Habitat Provider: The crusty surface of wart lichen provides microhabitat for tiny organisms, including bacteria and other microbes that form the foundation of ecosystem food webs.
Air Quality Indicator: Lichens are sensitive to air pollution, so their presence can indicate relatively clean air quality in your garden area.
Low Maintenance Ground Cover: If you’re looking for something that requires absolutely zero care on stone surfaces, wart lichen fits the bill perfectly!
Should You Encourage or Remove Wart Lichen?
This depends entirely on your gardening philosophy and aesthetic preferences. Wart lichen is completely harmless to plants, structures, and humans. It doesn’t damage stone or concrete – in fact, it can actually help protect surfaces from weathering by forming a protective layer.
If you appreciate a more naturalistic garden aesthetic and enjoy observing the subtle beauty of these ancient organisms, there’s no reason to remove wart lichen. However, if you prefer a more manicured look for your hardscaping, you can gently scrub it away with a stiff brush and water.
Living Alongside Wart Lichen
The beauty of wart lichen is that it requires absolutely no maintenance from you. It grows slowly, doesn’t spread to living plants, and quietly goes about its business of existing. It’s particularly resilient to urban conditions, pollution, and temperature fluctuations, making it one of nature’s most reliable colonizers of human-made surfaces.
If you’re designing a naturalistic rock garden or working with existing stone features, consider leaving patches of wart lichen intact. They add authentic character and demonstrate the incredible adaptability of life in urban and suburban environments.
So the next time you spot those warty gray patches on your garden walls, take a moment to appreciate this remarkable partnership between fungus and algae that’s been thriving on Earth for millions of years. Sometimes the most interesting garden inhabitants are the ones we never think to plant!
