Linked from
The 17 pages that link to Root nodule, each with the reason it gives.
CowpeaRelated: Cowpea roots form nodules with nitrogen-fixing bacteria.
Vicia fabaRelated: Faba bean nodules provide a habitat for bacteria that fix nitrogen.
FabalesRelated: Legumes in Fabales often form nodules to support bacterial nitrogen fixation.
LupinusRelated: Lupin roots form nodules that support bacterial nitrogen fixation.