It’s easy to miss lichens during the summer. At least here in the north, they have to compete with the riotous growth of green plants that have only a few short months to do their thing. Lichens really come into their own in winter, when the bare landscape lets them shine. When I was hiking a few weeks ago, lichens were among the most eye-catching subjects along the trail. Suddenly, with the trees bare of leaves, lichens are conspicuous everywhere.
When you start looking at them more closely, lichens are fascinating. For starters, a lichen is actually a two-part harmony of a fungal host and an algae. Sometimes a cyanobacteria also plays a role. Some twenty percent of the world’s fungi grow only as part of a lichen partnership. To put this symbiotic relationship very simply, the fungus provides shelter for the algae, while the algae provides food. The fungus benefits more from this relationship. While the algae could survive without the fungus, lichen fungi are never found growing alone.
Lichens grow on a variety of substrates: the ground (including decomposing logs), rocks (including surfaces such as roof shingles) and on trees. The two photos above show examples of a common rock lichen, rock shield lichens of the genus Xanthoparmelia
Rock shield is a foliose lichen, a lichen that looks like leafy growths divided by lobes. The lower surface is often differently coloured from the upper surface. Another example of a foliose lichen found on rocks is Rock Tripe (Umbilicaria spp). Rock tripes feature large, leathery lobes that look like they are peeling off the rock.
Here’s another rock tripe.
I also came across patches of reindeer moss (Cladina spp). It’s not a moss at all, but another lichen. Reindeer lichen is an example of a fruticose lichen, which have bushy or shrubby growth forms. As the name suggests, reindeer moss is an important food source for reindeer and caribou.
Reindeer moss grows over thin soils and rocks. Several different Cladina species may be found growing together.
Lichens that are very flat, appearing to be almost sprayed on a substrate, are termed crustose lichens. Powdery goldspeck (Candelariella efflorescens), which grows in small, round patches, is an example of a crustose lichen. Tree bark may feature whole communities with multiple species of lichens.
Some lichens only grow on specific tree species, while other lichens are generalists. Common greenshield (Flavoparmelia caperata) is a generalist that, as the name suggests, is extremely common.
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