If a mushroom is growing in a vineyard, does that constitute Kilaei HaKerem (forbidden mixture of plant species in a vineyard) considering that it is not growing from the soil? What if it is growing on a rock outcropping in the vineyard so that it isn't even touching the ground?
A number of points:
Kilaei Zeraim applies to things that grow from the ground. Mushrooms do not qualify.
Kilaei Zeraim is forbidden only if you plant it intentionally OR if you leave it that after you find it and it grows to maturity.
Kilaei Zeraim requires at least TWO different types of seeds to be planted in addition to the vine itself.