What are some benefits to sori being placed on the underside vs on top?

Question

*specifically fern

Answer 1

protection possibly? ways to identify it??

Answer 2

Well, since most ferns live in wet areas, probably having sori on the underside of the leaf provides some sort of protection for the sori from weather. I would also imagine that gravity would help them be dispersed more easily if they were on the underside of the leaf rather than on the top. Lastly, since most ferns also live in shadier areas, they need to be able to collect as much light as possible and so don't need sori blocking their main photosynthesizers (the top side of the leaf). This is just a guess, albeit an educated guess.