Discussion
Here, we presented the first formal hypothesis test of links among the evolution of root traits, leaf traits, and mycorrhizal state in seed plants and its main clades. Our results indicate that the substantial evolutionary shifts in root diameter and SRL of seed plants were correlated with leaf traits that facilitate enhanced hydraulic capacity and greater photosynthetic performance in the canopy, but also with changes in growth form. The reconstruction of trait values across the phylogeny suggest that switches to ECM associations could have impacted the morphology of Gymnosperm root systems, but had limited influence on Angiosperms. Indeed, Rosids and Asterids apparently evolved thinner, longer root systems before the evolution of ECM or Ericoid associations. Similarly, the evolution of the NM state associated with additional decreases in diameter and RTD, plus increases in SRL in Angiosperms, but those changes were also correlated with transitions from woody to herbaceous habit.