I see where Symphytum officinale (comfrey) was listed as a nitrogen fixer. To my knowledge it doesn't have legume nodules. Does the NF classification extend to plants without nodules but still have excess nitrogen to give an perhaps other forms? If so I think honey locust ( Gleditsia triacanthos) might fall under that classification.

I think N fixing should be limited to those who use rhizzobia symbiotically to fix nitrogen.

I agree that comfrey is not a N fixer. This error was made by me - my book 'Gaia's Garden' shows comfrey as a nitrogen fixer and I checked it off in our database without thinking. I'll remove it from the comfreys.

I'll the change for Achillea millefolium.

Excellent.

Azolla is a nitrogen fixer the that does so through a symbiotic relationship with a cyanobacterium (Anabaena azollae). Some Asian countries use it as a fertilizer in their rice. There have even been trails as a supplemental feed for livestock. Some trials have shown and increase in milk in dairy cows and eggs in chickens.

Soybeans?