Answer: If it looks like a mushroom, it probably is. But it shouldn't cause you alarm. Mushrooms of all kinds grow in moist soil that's rich with organic matter. As long as your lily looks healthy, it isn't at risk from the mushroom growth. About the only way to stop the growth and not harm your lily is to repot your lily in fresh potting soil. If it's in the ground, simply rake away the top inch or so of organic material that's on top of the soil and replace it with fresh mulch material.
Best wishes with your garden!
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