Fig. 1.

We explored the evolution of various alternatives to interacting with AM fungi, the ancestral state of seed plants. Examples of six important alternatives we considered are depicted, with columns indicating two potential pathways toward evolutionary breakdown of the plant–AM mutualism. In both pathways, the ancestral mutualism with AM fungi breaks down. Colored borders match colored bars in Fig. 2, indicating distribution of these traits across global seed plants. Image of AM fungi courtesy of Yoshihiro Kobae (Rakuno Gakuen University, Ebetsu, Japan). Other images courtesy of (Clockwise from Top Right) Pixabay/PublicDomainPictures; adapted with permission from ref. 69; Pixabay/Egle_pe; Euan James (The James Hutton Institute, Dundee, United Kingdom); adapted with permission from ref. 70; and Wikimedia Commons/B. Zak.