This question intrigued me as I did not know. I have always known that mushrooms are low in calories and full of fibre and protein. They are highly nutritious and good for you. I often enjoy eating them for breakfast and dinner. But do they have magnesium in them?
In my fun online fact finding search on mushrooms was most rewarding and helpful. I read that mushrooms contain potassium, selenium, B vitamins and copper. They even contain vitamin D if they have been grown in the sun. But, there is no magnesium in mushrooms!
There have been tons of research carried out on the health benefits and healing powers of mushrooms. I read that they are purported to help in the healing of cancer, diabetes, blood pressure, cholesterol and weight loss.

All mushrooms are good for you but there is a list of mushrooms that have the most benefits. Some of these are *golden oyster, shiitake, oyster and maitake.
In fact, research has identified more than 200 conditions that may benefit from mushroom consumption and more than 100 different beneficial effects they can produce for the body.source
It is recommended that mushrooms are cooked because they contain a natural toxin called Agaratine. source
A real tick from me with mushrooms is that they are not only highly beneficial health wise they clean also our earth. tHow incredible.
Mushrooms and the health of our planet
Mushrooms are good for you. And they’re also good for our planet. As world-renowned mycologist Paul Stamets discusses, mushrooms can potentially solve some of our most pressing and serious problems.
Clean up oil spills all over the world
Absorb farm pollution
Fight off smallpox and flu viruses
Combat insects
Create rich environments for farms and new forests, and
Become a sustainable fuel source for the future
source

This was a fun bit of research and now I can say that I am more informed on mushrooms. But, I did find that magnesium is in dark chocolate so an extra good reason to eat this yummy food.
Cheers and blessings