Fig. 2.

Mean enrichment factors ε¹³C and ε¹⁵N ± 1 s.d. of two Epipactis species associated with rhizoctonia fungi (yellow circles; Egi = E. gigantea, Epa = E. palustris), two Epipactis species associated with ECM basidiomycetes (light green squares; Ehn = E. helleborine ssp. neerlandica, Epu = E. purpurata), four Epipactis species associated with ECM ascomycetes and basidiomycetes (dark green squares; Eat = E. atrorubens, Ehe = E. helleborine, Efi = E. fibri; Emi = E. microphylla) and four Epipactis species forming orchid mycorrhizas exclusively with ectomycorrhizal ascomycetes (purple diamonds; Edi = E. distans, Ele = E. leptochila, Emu = E. muelleri, Ene = E. neglecta). All open symbols indicate isotope data extracted from the literature (Tables S2). The green box represents mean enrichment factors ±1 s.d. for the autotrophic reference plants that were sampled together with the Epipactis species (REF, n = 296, see Tables S1 and S2) whereas mean ε values of reference plants are zero by definition. The red box represents mean enrichment factors ±1 s.d. of all partially mycoheterotrophic orchid species associated with ectomycorrhizal fungi (ε¹³C_mean = 3·18 ± 2·38 and ε¹⁵N_mean = 9·61 ± 4·40) published since 2003 that were available from the literature (Hynson et al., 2016).