Linked from
The 9 pages that link to Sorus, each with the reason it gives.
FernBroader topic: Its placement and appearance often reveal where a fern makes spores.
FrondBroader topic: Sori are visible reproductive structures on many fertile fronds.
PteridophyteBroader topic: Many ferns group their sporangia into visible sori.
BrackenBroader topic: Bracken produces spores in sori along the margins of its fronds.