In honour of Halloween, let’s look at something that can make PEI’s trees look decidedly eerie: Old Man’s Beard Lichens (Usnea spp.)
Lichens are among my favourite organisms. They can be found on every continent (including Antarctica), at elevations from sea level to mountaintops, and in habitats from rainforests to deserts. Several types of lichens – including some of Sunburst Lichens (Xanthoria spp.) that can be found here on PEI – were placed outside the International Space Station where they were exposed to the vacuum of space and the sun’s unfiltered radiation for a year and a half; they returned to Earth just fine.
Lichens are sometimes confused with mosses. To make matters worse, Usnea in particular is often mistaken for Spanish Moss (Tillandsia usneoides) which isn’t a moss at all, but rather a flowering plant in the Pineapple Family. Confused yet?
Mosses are ancient, primitive plants but lichens aren’t plants at all: they are fungi and algae living together and functioning as individual organisms. Fungi can’t photosynthesize and so need to get their nutrition elsewhere. Many form relationships with living plants, trading water and nutrients for sugars the plant makes from sunlight. Others feed on dead plants and animals, or other organic matter. But some partner with photosynthetic algae and form lichens.
When I first studied biology about 35 years ago, lichens were described as two equal partners living in a mutually beneficial relationship. Despite what we might like to believe, nature is more often a brutal fight for survival than gentle cohabitation. We now know that lichen relationships are much more complex and varied, and that the algal partner is usually damaged to some degree by the fungus. This can range from creation of relatively minor ‘leaks’ in the algal cells so the fungus can steal the sugars, to outright invasion that kills the algal cells (albeit more slowly than new cells are produced so the lichen itself continues).
The relationship isn’t entirely one-way. Fungi do provide protection and moisture to their algal partners and enable them to live in habitats that they otherwise couldn’t. Even so, in most cases the fungus can’t survive without the algae, but the algae could live on their own provided enough moisture were present. I’ve seen lichens described as ‘fungi that are farming algae’ which probably isn’t a bad way to look at it.
There are at least 10 species of Beard Lichens expected to occur on PEI, but with so few people able to confidently identify them to species not much is known about their abundance and distribution. They range from the well-named Methuselah’s Beard Lichen (Dolichousnea longissimi) which can be three metres (10 feet) long to the tuft-like Bristly Beard Lichen (Usnea hirta) that’s typically under five centimetres (two inches).
One feature common to all Usnea lichens is that they have an elastic, central cord. If you have what you think is a Beard Lichen, gently pull apart a strand and look for that distinctive centre. Its size and colour can also help with identification to species in some cases.
Usnea lichens were traditionally used to treat skin, mouth, and throat infections, as well as bronchitis, tuberculosis, and other ailments. Modern research has shown strong anti-bacterial properties of the lichens’ usnic acid, along with anti-viral, anti-fungal, and anti-tumor effects. However, it has also been linked to liver damage and so is best kept to external uses.
As organisms that get all their moisture and nutrients from the air, Lichens can be particularly sensitive to air pollution; the presence of lush, healthy lichens is often an indicator of good air quality. The beautiful Beard Lichens shown here (as well as the several other types growing on this tree) are good signs for PEI untamed!
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