What's the difference between lichen and fungus, like mushrooms? Thank you.
Hoo boy, that's the question, huh?
So, fungi are a lot of things. "Fungi" is an entire kingdom of life, like "Plantae" (plants) or "Animalia" animals. Consider how much diversity there is within those 2 groups, and now shift your perception of what a fungi can look like to that level of complexity. In, say, animals, those complex differences are pretty obvious when looking at like, a clam vs a honeybee vs a crocodile vs a human. But in fungi, most of that complexity isn't super visible to the human eye because most fungi are small and cryptic, so it gets overlooked even though the diversity is there.
"Mushrooms" are the fruiting bodies of basidiomycete fungi: just one division of the entire fungal kingdom. A fruiting body is like, well, a fruit! It is a reproductive structure that releases spores, which are like the seeds of plants. These structures are attached to a "mycelium," a connected network of fungal hyphea (long filaments containing fungal cells). Think of the mycelium as like, the trunk of a tree, and the mushroom as an apple.
Not all fungi have a mycelium (the same way not all plants have a trunk)--many are unicellular organisms, and others have simpler body plans, and some (like lichens) have more complicated body plans.
Besides basidiomycete mushrooms, ascomycete fungi produce mostly "cup-shaped" fruiting bodies, often referred to as "mushrooms" even though they aren't technically mushrooms.
Confused yet? Stick with me.
What is a lichen? Lichenization (a fungus forming a symbiotic relationship with a photosynthesizing organism) is a lifestyle trait more than it is a distinct group. While most "lichens" are ascomycete fungi, there are some basidiomycete fungi that have lichenized as well. It is a way for a fungi (we call it the mycobiont) to basically "farm" algae and/or cyanobacteria (we call these the photobionts) to harvest energy from, and in return the mycobiont provides the photobiont with a safe environment.
Most lichens have "apothecia" as seen in the picture above: the cup-shaped fruiting bodies often found in the ascomycete fungi. BUT some (very few) lichens actually *have* mushrooms because they are a symbiosis between an algae and a mushroom-producing fungi (basidiomycete):
SO to conclude:
--Fungi is a diverse kingdom of life
--Mushrooms are a reproductive structure of a specific lineage of fungi
--Lichens are a symbiotic organism made up of a fungus and a photosynthesizing organism (algae and/or cyanobacteria)
--Most lichenized fungi are ascomycetes, but some are basidiomycetes
--You can think of lichenization as a lifestyle as opposed to a specific group
Fungi are complicated and difficult and confusing, and wonderful and beautifully complex and endlessly fascinating!