What’s that stuff on my tree? A guide to Manitoba’s lichens
If you’re an observant person, you may have noticed colourful things growing on Manitoba’s trees and rocks. Although some of these organisms are mosses (especially near the base), they are more likely to be lichens. Bright orange firedot lichens are common on Manitoba’s elm and oak trees.
Dog lichens are common on moist, forest floors. (Photo courtesy of Manitoba Museum)
Lichens are symbiotic organisms; they consist of a fungus and an alga. In some lichens, there is also a cyanobacteria or a second or third species of algae (there are still a lot of unknowns when it comes to lichens). Common dog lichens typically have cyanobacteria in them, often from the genus Nostoc, a free-living species that looks like bits of crumbled tar when dry. The algae and cyanobacteria, if present, photosynthesize, producing sugar, which they share with the fungus. The fungus absorbs water and dissolved minerals directly from the environment (so it doesn’t need any roots) and shares it with the other species. Cyanobacteria can also take nitrogen gas from the air, turn it into a chemical form and share it with the other partners.
Where do lichens grow in Manitoba?
Crustose lichens grow on rock outcrops in places like Whiteshell Provincial Park, MB. (Photo courtesy of Manitoba Museum)
Lichens grow in the patterns that they do to maximize the amount of light they intercept. Some species look like tree branches (called fruticose = branch-like lichens) for this reason. Other lichens are leaf-like (called foliose) or crusty (called crustose). Some lichens living in really harsh environments (like the Antarctic) are cryptoendoliths, meaning that they live inside the rock, penetrating the tiny spaces in between rock crystals.
In the Prairies, lichens often grow in hot, sunny habitats, such as sandy soils, and on glacially-deposited rocks. They are also common on fence posts and abandoned human artifacts, like collapsing homesteads and rusty ploughs.
In the Prairies, reindeer lichens often grow along with creeping juniper on dry, sandy soils. (Photo courtesy of Manitoba Museum)
In forested areas, lichens are common, growing on trees, as well as mossy, forest floors. In the Canadian Shield, rock outcrops are often almost completely covered by lichens. In urban areas, lichens are sometimes found on old buildings, like the legislature. Different species grow on these different substrates (hardwood versus softwood, sandy soil versus clayey soil, granite versus limestone), so make sure you record this information when trying to identify lichens.
Lichens are often the first organisms to start growing on disturbed soils. (Photo courtesy of Manitoba Museum)
Since they don’t need soil, lichens are some of the first organisms that begin growing after large disasters wipe out all the vegetation in an area. They are often the first to arrive after hot fires or mining activity. Acids in the lichens break down rocks, contributing to soil formation. Lichens can completely desiccate when they are dry, growing again when it rains. Due to this periodic desiccation, lichens tend to grow very slowly and reach extremely old ages. Some lichens can be aged the way trees are — by counting their growth rings. Some, such as yellow-green map lichens, have been dated as being over 8,600 years old.
Lichens reproduce themselves vegetatively by breaking off into tiny pieces, and both sexually and asexually. Sexual fruiting bodies of various kinds are produced by the fungus. They release small, single-celled spores, which germinate into new, partner-less fungi. These tiny fungi must find free-living alga to become lichens again. To allow both the fungus and the algae to disperse together, lichens also produce asexual propagules (i.e. tiny clusters of cells, often dispersed by wind, that will grow into a new lichen). They are usually at the branch tips
A few of the most common lichens in southern Manitoba are described below:
Pebbled pixie-cup lichen
Pebbled pixie-cup lichen (Photo courtesy of Manitoba Museum)
Pixie-cup lichens were so named because ancient Europeans thought that fairies or pixies would use these structures as goblets to drink from. The “cups” are actually the lichen’s reproductive structures. This species is found in all provinces, occurring on forest floors and sometimes tree bark.
Specimen of reindeer lichen, catalogue number L-657 (Photo courtesy of Manitoba Museum)
As the name implies, this species is eaten by “reindeer,” called caribou in Canada. Reindeer lichens are common in the Arctic and boreal forest, but are also found farther south. In Manitoba’s prairies, they are most common on sandy soils. This fruticose lichen grows sexual and asexual structures at the very tips of its branches. Vegetative reproduction via fragmentation is also a common method of spreading, as the branches are fragile when dry.
Sand-loving Iceland lichen
Sand-loving Iceland lichen (Photo courtesy of Manitoba Museum)
Like reindeer lichen, this species is found on sandy or thin soils in the Prairies. However, it is a prairie specialist and not found farther north. You can find it on the sand dunes near Portage la Prairie, Oak Lake and Carberry. It is a fruticose lichen with some flattish portions and upturned, spiny margins. This species reproduces mainly vegetatively via fragmentation or the production of asexual propagules. Sexual reproduction is infrequent, with the spore-producing structures located at its tips.
Specimen of rosette lichen, catalogue number L-664 (Photo courtesy of Manitoba Museum)
Species in this genus grow on alkaline substrates, such as calcareous, siliceous and basaltic rocks, bones, bark and soil. They often grow on substrates that are high in calcium, nitrogen and phosphorus, such as places where birds like to stand and poop. For this reason, they have been called ornithocoprophiles (any organism that grows or thrive in bird feces). They are foliose lichens that grow in a rosette, and they mainly produce asexual propagules on their upper surfaces.
This blog is adapted from the original post on Manitoba Museum's blog and is reposted with permission.