I Like Lichens!
Lichen is one of the more common organisms living in your very own yard or local park, but we tend to look right past it most of the time. I found some on my neighbor’s mailbox:
This is the common greenshield lichen, aka Flavorparmelia caperata, which is native to the U.S. We see it everywhere growing on trees and rocks, but you probably never think very much about it. Somewhere along the way, you may have learned that it is a combination of two forms of life…or…something like that. Well, if you need a quick refresher, here’s the scoop:
One part of every lichen is always a fungus. Another part is either an alga (algae make their own food via photosynthesis, but are not plants), OR a cyanobacterium (a.k.a. “blue-green algae”…a type of bacteria that can photosynthesize, and produces oxygen). The structure of the lichen, provided by the fungus, allows for moisture collection, and the algae or cyanobacterium creates food from the sun for the lichen. For almost 150 years of staring at lichens through microscopes, scientists have believed that only two organisms made up lichens. Science teachers across the globe held up lichens as a perfect example of symbiosis in nature (symbiosis is a relationship that benefits both partners).
BUT…in 2016, scientist Toby Spribille published a discovery that will cause biology textbooks to be rewritten: there is a third organism included in the makeup of lichens: YEAST. (Yeasts are members of the Fungi kingdom). See, he and symbiosis specialist John McCutcheon had been examining two different lichens, Bryoria tortuosa (yellow, produces toxic vulpinic acid) and Bryoria fremontii (dark brown, does NOT produce the toxin). They looked very different, but genetic testing said that they were identical…the same fungus was pairing with the same alga. It took Spribille a while to figure out that genes from basidiomycete fungus were also being activated there…they thought the basidiomycete was just contaminating their lichen samples. It turned out that the basidiomycete fungus was actually what was responsible for the vulpinic acid of Bryoria tortuosa! He started screening lichen samples from all over the world…and in almost all those macrolichens, he found the genes of basidiomycete fungi. They were everywhere. The field of lichenology has been completely turned upside down…if you take a quick Google, you’ll see that websites all across the Interwebz STILL need to be updated.
So now the next generation of schoolkids will learn that lichens are not just a “happy couple” pairing of a fungus and an algae…lichens are actually a happy threesome!
IS LICHEN BAD FOR MY TREES? No. Lichen are not causing any harm to your trees or any other surface they are growing on. However, lichen do tend to grow in larger numbers on trees that are already in trouble, because trees with fewer or no leaves are getting more sunlight to their bark, where the lichen grows. Lichens only grow on the tough outer layer of tree bark. The xylem and phloem (food and water transportation tubes) of the tree are well-protected within the innermost layers of bark.
To learn a little more about lichens for your next party conversations: https://www.fs.fed.us/wildflowers/beauty/lichens/biology/growthforms.shtml
For further reading on the amazing yeast-lichen discovery: https://www.purdue.edu/newsroom/releases/2016/Q3/yeast-emerges-as-hidden-third-partner-in-lichen-symbiosis.html
Thanks for learning with me...hope to see you outside!