Fern spores that are clustered in small dots or stripes on the undersurfaces of the frond are called

• A. Sori
• B. Pinnae
• C. Indusia
• D. Prothalli

Answer: (A)

Sori are the clusters that produce and house fern spores. On the undersides of fern fronds, the sporangia (the structures where meiosis happens to make spores) are grouped into these localized dots or stripe-like patterns, which appear as brown or tan spots as they mature. The term sori captures this clustered arrangement and is what you’re seeing when you notice spores concentrated in small groups on the leaf underside.

Indusia are the protective coverings that can overlie sori in some species, so they relate to how the sori are protected rather than to the basic clustered pattern. Pinnae are the leaflets of the frond, not the spore-producing structures. Prothalli are the separate, free-living gametophyte stage of ferns that develops from a spore, not the clusters themselves.