Are Fungi in Lichens Parasitic?

I am studying lichens and the relationship between fungi and algae/cyanobacteria. Most articles say the fungi and algae/cyanobacteria in a lichen mutually benefit each other, living in a symbiotic relationship. The fungi provide shelter and algae provide food/energy.

I came across a few videos and articles that pointed out that the fungi could be considered parasitic because it is too dependent on the algae partner. When separated, the algae can continue to live by providing food itself. The fungi, on the other hand, rely on the algae for their food. Unlike other fungi, “lichenized” fungi can’t feed off decaying organisms and will eventually die when separated form the algae. In this relationship, the fungi benefits more and actually steals nutrients from the algae.

Is this true? Could the relationship between lichenized fungi and algae then be considered a controlled form of parasitism?

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in parasitism only one of the two parts receive a benefit from the relation, and the other receive a damage
in symbiosis both parts receive a benefit from the relation
in commensalism only one parner receive a benefit, but for the other is indifferent
and exist a shade of grey between these three types

the algae receive a benefit because of the shelter that protect her from the disseccation, and this enlarge their environmental fitness and increase the types of habitats that they can use.


In studies where they’ve separated the algae and fungi usually both (or more, sometimes it’s more than 2 partners), both the fungi and algae are generally able to survive and grow independently without major problems. The fungi have a wildly different growth form when not part of a lichen and are unrecognizable as being a lichen forming fungi by visual observation when they’re grown separately.

Generally the relationship is considered to be one of mutualism, not parasite and host.


I agree with those who doesn’t call it a mutualism, with the way fungi catch algae, and as I remember a synthesizing organism is living worse than when alone.

I took a short field course on mosses and lichens that assigned this as background reading:

I really liked the readings b/c it challenged how I thought about lichens, thinking about the “double status of lichens as organisms and ecosystems,” and the broader natural world. Sort of trippy.

Lichens, he argues, have relevance far beyond their interest as objects of scientific inquiry. Lichens exist at a doorway, a portal. Look out this doorway in one direction and what you see is ecosystem – a collective of unrelated species, fungus and alga and bacteria. But look out the same doorway in the other direction, and what you see now is organism, in a sense no different from any other macroscopic organism.


What’s fascinating is that many organisms could be considered ecosystems in their own right – humans, for example! But that’s a bit off topic

Thanks for the info! Do you have a link to the study or know what it’s called? I’d like to use it for my project!

This is actually something I was wondering about recently - are the lichen-forming fungi considered a different species if they’re growing without the algal partner, or vice versa? Theoretically, if they can grow and reproduce separately, it seems they ought to be.

Although it would probably be considered cheating to observe every lichen 3 times for the lichen, the fungi, and the algae species ;)


@LittleLichenLover - Look up ‘axenic cultures of mycobionts’.

There are a lot of papers on the subject, but here’s a recent one that should get you started and provide a lot of follow-up papers in the references portion.

@graysquirrel - this paper addresses that exact question:


Not if you see them separately. Do lichen-forming fungi occur in the wild without their algae?

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Thats a really good question! I’ve read a couple of articles and it seems that in some cases lichenized fungi are more parasitic in nature than symbiotic, but I also think that its not always the case. I think in most species/scenarios the fungi and algae have a symbiotic relationship with the fungi using the sugars to create the structure of the lichen, and that helps the lichen survive in the environment (and thus the algae in the lichen).

I also think that relationships within lichen in general are so interesting, I learned first about lichen because of an article published by Purdue in 2016 (here’s the link to the study/article and they talked about a study in which they found a third organism in some species of lichen. It was yeast, and although it’s also a fungus it was a completely different type of fungus than what usually partners with lichen. I highly recommend you check out the article, its super informative. It also makes me wonder if yeast is more parasitic than symbiotic in some cases since its also a fungi or if it has any impact on the relationship of organisms within lichen in the species it inhabits.


Thanks! Will definitely check this out!

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