A long time ago I saw what must have been mycorrhizae on, of all things, Ceratophyllum, which does not have roots. I grew some in a gallon jar with soil on the bottom, and, later, when I removed the plant, gobs of mud clung to the stem where it had been pressed into the surface. I washed away the mud and found a dense mat of colorless half inch hair-like threads coming from the stem and even from the leaves. Under the microscope these threads looked like fungal hyphae. I could clearly see the cross walls separating the cells.