The plants on this list are reported to have symbiotic relationships with nitrogen fixing organisms, typically cyanobacteria species.
Rai, A.N. et. al., Tansley Review No. 116 Cyanobacterium–plant symbioses, New Phytologist, Volume 147, Issue 3, September 2000 , pp. 449-481. Document may be behind paywall. Last accessed on Thursday, November 09, 2017.