Nitrogen isotopes reveal independent origins of N2-fixing symbiosis in extant cycad lineages

Michael A Kipp^*, Eva E Stüeken, Caroline A E Strömberg, William H Brightly, Victoria M Arbour, Boglárka Erdei, Robert S Hill, Kirk R Johnson, Jiří Kvaček, Jennifer C McElwain, Ian M Miller, Miriam Slodownik, Vivi Vajda, Roger Buick

^*Corresponding author for this work