12/20/2025
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Lichen is one of the easiest living things to overlook — and one of the most fascinating once you notice it.
Those soft greens, pale grays, and powdery patches on tree bark aren’t dirt or moss. They’re lichen, quietly growing right in front of us, creating a miniature world on branches, trunks, and stones.
Lichen isn’t a single plant. It’s actually a partnership between two organisms: a fungus and an alga (or sometimes cyanobacteria). The fungus builds the structure and offers protection, while the alga produces food through photosynthesis. Neither could survive as well on its own — together, they form something entirely new.
If you look closely, lichen grows in a few distinct forms.
Leprose lichen is the powdery kind. It often looks like it’s been lightly painted onto bark. These lichens lack a smooth outer layer, so they appear dusty or granular, made of loose fungal threads and algal cells. Despite their soft look, they’re surprisingly good at repelling water.
Foliose lichen is the leafy kind. It forms lobes that resemble tiny leaves or wrinkled paper. These lichens have a clear top and bottom and attach to branches with fine, root-like structures called rhizines. Sometimes the edges even lift slightly off the bark.
Fruticose lichen is the shrubby or stringy kind. These grow upright like miniature bushes or hang down like hair. Because they extend out into the air, they absorb moisture directly from the atmosphere and are especially sensitive to environmental conditions.
That sensitivity is what makes lichen so important.
Lichens absorb everything from the air around them — nutrients and pollutants alike — which is why scientists use them as natural indicators of air quality. When you see leafy foliose or bushy fruticose lichen thriving on branches, it’s usually a sign the air there is relatively clean.
So the next time you pass a tree, slow down and look closely. Lichen may be small and quiet, but it tells a much bigger story about the health of the world around us.
