A lichen threesome

It's February, and Valentine's Day is upon us. Everyone is thinking about that significant other. That significant other is usually a single person in a monogamous relationship, although many variations are known in human cultures. Once you look outside the human species, anything goes. No matter how weird certain constellations might seem, they have been invented already, by animals, plants, fungi, millions of years before humans appeared on Earth.

Lichens are no exception, and here is one of the most spectacular threesomes known in the lichen world. Most lichens are dual symbioses, composed of a fungus and a photosynthetic alga or cyanobacterium. Certain lichens come as threesomes, with one fungus associating with both a green alga and a cyanobacterium. This lichen is even weirder, as it has two fungi sharing one alga. The main fungus or the "spouse", if you so will, is a basidiomycete related to the Fire Sponge (Phellinus ignarius), and its name is Marchandiomphalina foliacea. Its fruiting bodies are unknown. Instead, the tiny globose fruiting bodies belong to second fungus, the "lover", an ascomycete distantly related to the Blue Cheese Mold (Penicillium roquefortii), with the name Norrlinia peltigericola.

Now, rarely do spouse and lover cohabit without quarrel, although in some human societies this is common practice. In this lichen, the two fungi seem to get along well, and the alga appears to enjoy the presence of its two companions. What can we learn from this? Unconventional relationships don't have to be complicated!