What is the term for the structure on the underside of a fern frond that produces spores?

The structure on the underside of a fern frond responsible for producing spores is called sori. Sori are clusters of sporangia, which are the containers that hold the spores. They typically appear as small brown or orange spots on the frond and are crucial for the reproduction of ferns. When the spores are released from the sporangia, they can disperse and potentially germinate to form new fern plants, continuing the life cycle of the fern.

Understanding sori is essential in studying ferns and their reproductive strategies, as they allow for the formation of the gametophyte generation, which is an important part of the fern life cycle. This term is key in botany and horticulture, particularly when discussing the anatomy and life processes of ferns.