Lichens are a symbiosis between 3 organisms

[Plazma Inferno!]

For over 140 years, lichens have been regarded as symbiosis between fungi and algae.
But scientists have made the new discovery that many lichens are also made up of a previously undiscovered third partner — a new kind of yeast.
Not only does that potentially alter the fundamental definition of what a lichen is, but it "should change expectations about the diversity and ubiquity" of the organisms that form them, says a new study.
The new yeast has apparently gone undetected in lichens for more than a century, despite the fact that scientists all over the world have devoted entire careers to studying lichens closely with microscopes and genetic testing.
That seemed so unlikely that the scientists working on the project had trouble believing it themselves.
Toby Spribille, lead author of the paper, said he and his colleagues had to check their data more than 10 times to be sure.

http://www.cbc.ca/news/technology/lichen-yeast-1.3689468

Study: http://science.sciencemag.org/content/early/2016/07/20/science.aaf8287

 

[iceaura]

The lichens involved apparently can exist without the yeast - it's not a fundamental constituent in some sense. But the example mentioned gained a serious benefit from harboring the yeast in its cortex - it became inedible to a major predator. And this inedibility was advertised in the phenotype alteration. So I'm wondering whether this actually changes the fundamental description of the lichen itself.