Q.Cause Of Damage To Magnolia Tree?
I’ve discovered damage to the trunk of my Magnolia tree. As well as there being multiple splits on the bark, there are also a lot of small (8-10mm) black pyramidal things next to it stuck on the bark. Pictures attached! The split seems quite deep. So two questions : any idea what’s causing the damage and any advice on remedial steps? Thanks in advance.

Certified GKH Gardening Expert
This looks to be a mushroom! I see gills. Unfortunately, I cannot ID this one.
It could be that this mushrooms has caused the damage that you see, or it could be that it is taking advantage of the damage done by something else.
Either way, if you are noticing cracks this deep in the bark, it may mean that your tree is in decline.
You may attempt correction with a fungicide, but you may be watching your tree die, slowly, unfortunately.
Here is an article that will help:
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm