Horticulturists make bad jokes all of the time...who can forget the wildly popular, 'with fronds like these, who needs anemones ...?' And then there are plays on the words 'you' and 'yew'...although not even one joke about them comes to mind as I write this...brain fog from covid? We can blame everything on COVID, it seems, even if we have not yet had it! Maybe I'll remember a particularly bad joke about yews (or is it ‘youz’) before I have finished this posting...I know you are waiting with bated breath for that one...!
And then there is a favourite joke of mine, 'Did you hear the one about the algae and fungus? They were out in the woods when they met, and right away they took a 'lichen' to each other.'
Moss (green plant) and lichens together on boulder above Meech Lake.
Now, we have all seen lichens on trees and rocks and ornamental garden sculpture, often in damp conditions, but I would guess that most gardeners don't know anything about them. I never really knew much, or even thought much, about them, except that many would catch my eye from time to time with their bright colours and variety of structures, especially in the winter on the bare branches of deciduous trees. After a big wind like the one we had a couple of weeks ago, many twigs and larger branches came down, and while cleaning them up, I was surprised at the variety of lichen on each branch, so I started to dig a bit more.
A beautiful miniature world
Lichens are wonderful organisms. We don’t really see them much until we actively start looking for them, but when you finally open your eyes to their miniature world and the work which goes on there, well, it is nothing short of a miracle, and a relationship which merits more attention. So, here in a nutshell, is what you might find interesting about lichens.
1 ... they are organisms made up of an algae and a fungus.
2 .... These two components have a very special relationship called a symbiotic relationship, one of many types of symbiotic relationships in the plant and animal world. Lichen has, specifically, a mutualistic symbiotic relationship, where each organism benefits from the other’s presence. Some algae provide food from sunlight to the fungus – if it is green the algae contains chlorophyll, thus feeding the fungus - allowing it to carry on the important work of breaking down dead and decaying plant material. And some algae produce an acid which breaks down the minerals in rocks, providing food for the lichen. In turn, the fungus protects the algae from drying out by producing a covering to protect it. When the algae is kept moist, it works to absorb pollutants from its, surroundings. So, if your trees have lots of lichen on them, it is generally a sign that you live in a spot with less pollution.
3... Lichen also fixes nitrogen from the air – this means that it is able to take in nitrogen in the air surrounding it and process it in order to ‘make’ nitrogen - the fertilizer N, which all plants need for good, green growth. (Lightning fixes nitrogen as well, but on a smaller scale...It unlocks the nitrogen in the air when it flashes and splits apart the nitrogen molecules in the air, which then attach to oxygen molecules, which in turn falls with rain to fertilize the soil (...forgive me, I digress!)
4...Lichen is an epiphyte, often referred to as an ‘air plant’, or an organism which attaches to a surface – often tree branches for lichen – but which does not damage or otherwise affect the host. It draws its food and water from the air and rainwater around it, as well as from organic material in its surroundings., i.e. when the wind blows nutrients across the surface of the lichen. The tree to which the lichen attaches is merely used for support by the lichen. Mistletoe, in comparison, is a semi-parasitic air plant, as it does cause damage or at least might weaken the host by sending its roots into the vascular system of the host.
Many different lichens on one branch
5... There are three common types of Lichen
i) Crustose - a lichen which looks crusty and often rather flat – you cannot take the lichen off the tree or rock to which it is fastened without damaging it. Often found on wet rocks or on gravestones.
ii) Foliose – a leafy lichen. The leafy part can be removed from the substance it is attached to. One of the most common lichen found in a forest.
iii) Fruticose – a bushy-looking lichen which almost looks forest-like or shrubby, if looked at closely. Some of these lichen hang from branches and look a bit like Spanish moss.
Silver birch covered by lichen, NY State
Lichen on a gravestone, Japanese cemetery, Big Island, Hawaii
A couple of different types of Lichen on stone carvings in Central Park, New York
So, I hope you will delve further into the world of Lichens! The internet has a plethora of sites which show every colour and shape of lichen – more than you could ever imagine! Take some time on a dreary day (of which we have had many recently) to explore lichens in more depth. You will be astounded at how many there are out there, and that they are working hard to keep our environment clean and to break down decaying matter.
I found one site, for example, about lichens in Nova Scotia which said that there are 1000 different species of them in NS, which is more than all the species of birds, mammals, fish, amphibians and reptiles found in the province, combined. That’s pretty amazing...
A couple of other sites to look at...
https://inaturalist.ca/guides/9793
or google
Lichen Nova Scotia
Blue Rocks Park, Nova Scotia
Blog by Mary Pratte
All photos by Mary Pratte and are not to be used without permission