Long Before Trees Overtook the Land, Earth Was Covered by Giant Mushrooms
What an interesting idea, I can't help but visualize Zangermarsh[1] :-) Interesting question about what it might gain evolutionarily by being tall, perhaps more moisture exposure but as others have pointed out fungal mats get that by just being wide and covering a lot of area. Of course if you were competing with a fungal mat being tall might be one strategy.[1] Its a World of Warcraft zone