Extended Data Fig. 3. Alternative placements of the NEOCHROME constraint.

The NEOCHROME horizontal gene transfer is predicted to have occurred from hornworts into the ancestor of polypod ferns. However, topological uncertainty in the NEOCHROME gene tree allows the possibility that the transfer could have occurred into a more ancient lineage (A). We placed the relative node calibration such that hornworts must be more ancient than (i) Polypodiales (ii) Cyatheales + Polypodiales and (iii) Gleicheniales+Cyatheales+Polypodiales. The 95% highest posterior density (HPD) for the molecular clock analysis under each scenario is shown as a bar in (B), with a dot for the mean age. 95% HPDs were calculated from 2,000 post-burnin samples over 2,000,000 MCMC generations.