Data compilation and mycorrhizae classification
To examine the evolutionary changes in leaf and root morphology among
seed plants, we compiled trait data from previously published databases.
In the case of leaf vein density, we compiled information from Boyceet al. 2009 (257 species); Brodribb & Feild 2010 (272 species);
Walls 2011 (87 species) and Li et al. 2015 (80 species, see
Appendix 1 for a detailed list). Because “vein density” is defined as
the average distance between veins (usually secondary and higher orders)
within the mesophyll (Brodribb, Feild & Sack 2010), taxa with
single-veined leaves like Gymnosperms or parallel veins without
interconnections like most Monocots are lacking in this dataset. In the
case of root traits, we used data described in Valverde-Barranteset al. (2017) for diameter (D, mm), SRL (g/m), and RTD
*g/cm3) deposited in the Fine Root Ecological Database
(Iversen et al. 2017). Mycorrhizal state was binned into four
mycorrhizal groups based on the classification in Maherali et al.(2016): AM, ECM, transitional (AMNM) and non-mycorrhizal (NM) based on
consensus classification from previous studies. Species reported as AM
or NM in different studies were binned in the AMNM transitional stage
(Maherali et al. 2016). In order to simplify classification,
species that evolved to form associations with Dikarya fungi were all
classified as ECM (including ericoid mycorrhizal, ectomycorrhizal, and
dual AM and ectomycorrhizal species). However, considering the
substantial differences in root morphology and anatomical adaptation
differences between ECM and Ericoid species, all analysis in this study
were repeated with and without Ericoid species to confirm trends.