It’s another chilly, damp day in the temperate rainforest.
The mosses that hang from the trees drip slowly.
The streams run through the forest. Amongst the fallen branches, there are little greenish-grey bits of plants.
Some of them look vaguely like an exotic type of lettuce. Others are hard and lie flat on the branches.
What are these strange, plant-like green things?
They are lichens, and although they might look like plants, they are not. They’re plants… and they’re something more. If lichens had a Facebook status, it would likely be “it’s complicated.”
What is a Lichen?
Like the slime molds, lichens are a hybrid; a symbiotic relationship between an algae and a fungus.
There is a terrible joke in the naturalist community, and it goes something like this: a lichen is a fungus and an algae, and they’re likin’ one another. Terrible jokes aside, lichens consist of an algae called a photobiont and a fungus called a mycobiont. Together they form something a little bit different – something that allows both the algae and the fungus to live well.
How does this relationship benefit both parties? Most of the fungi in this relationship are not able to survive without an algal partner. Plants have a superpower that animals and fungi do not have: they can make their own food through photosynthesis. This is very useful for the fungal part of the lichen, since it needs this food to survive.The fungus harvests these sugars, sending out chemicals to help them diffuse through the permeable cell walls of the algae. Most of the algae can survive on their own, but they may need a very specific habitat in order to do so. By cohabiting with the fungus, the algae can live in many different environments and extend its range significantly.
Different lichens contain different kinds of fungi, and it is this that helps classify lichens into different species.
Lichens Are Tiny But Tasty
In the north, lichens are an important food source for caribou. Few plants grow in these areas, and the plants that grow well often grow in the short northern summers. In more southern areas where the winter snow makes it more difficult for animals to find food, the lichen that drops down to the top of the snow also a helpful source of food for hoofed mammals. Lichens are also good building materials for hummingbirds. These tiny birds use little bits of lichen in their nest-building activities.
Lichens Make Air Quality Visible
Lichens are useful to humans as well. They’re a good indicator of long term air quality, since certain lichens such as the Usnea species can only grow in areas with good air quality. Other species such as Parmelia and Physcia can grow in areas with poorer air quality. Mapping these lichens is useful to those who are trying to map air quality, and changes in lichen species can reveal changes in air quality over time. The US Forest Service has a lichens and air quality database.
Lichens: Small But Critical
While lichens may be small, they are an important food source and indicator species. These little hybrids are also a fascinating study of the complementary natural relationships that exist on a tiny scale.
Beck, A., Mayr, C. Nitrogen and carbon isotope variability in the green-algal lichenXanthoria parietina and their implications on mycobiont–photobiont interactions. (2012). Accessed November 26, 2012.
Environment Canada. Monitoring Lichens As Indicators of Air Quality. Accessed November 25, 2012.
Sharnoff, Stephen and Roger Rosentreter. Wildlife Use of Lichens. Bureau of Land Management. 1998. Accessed November 25, 2012.