What causes nodules on the roots of house ferns?

Nodules on the roots of house ferns are often caused by the presence of beneficial bacteria, such as nitrogen-fixing bacteria, which form symbiotic relationships with the plant. These bacteria can enter the root system and create swellings or nodules, aiding the fern in nutrient absorption, particularly nitrogen. Additionally, root nodules can also be a response to stress factors in the environment, such as poor soil conditions or root damage. Overall, these structures can reflect the plant's adaptations to its growing conditions.