• Background and Aims Mycoheterotrophy entails plants meeting all, or a portion of their carbon (C) demands via symbiotic interactions with root-inhabiting fungi. Ecophysiological traits of mycoheterotrophs, such as their C stable isotope abundances, strongly correlate with the degree of species’ dependency on fungal C gains relative to C-gains via photosynthesis. Less explored is the relationship between plant evolutionary history and mycoheterotrophic plant ecophysiology. We hypothesized that the C and nitrogen (N) stable isotope compositions, and N concentrations of fully and partially mycoheterotrophs differentiate them from autotrophs, and that plant family identity would be an additional and significant explanatory factor for differences in these traits among species. We focused mycoheterotrophic species that associate with ectomycorrhizal fungi from plant families Ericaceae and Orchidaceae.

• Methods We compiled published and unpublished data on the N concentrations, C and N stable isotope abundances (δ¹³C & δ¹⁵N) of fully (n = 18) and partially (n = 22) mycoheterotrophic species from each plant family as well as corresponding autotrophic reference species (n = 156) and used these data to calculate site-independent C and N stable isotope enrichment factors (ε). We then tested for differences in N concentration, ¹³C and ¹⁵N enrichment among plant families and trophic strategies.

• Key results We found that in addition to differentiating partially and fully mycoheterotrophic species from each other and autotrophs, carbon and nitrogen stable isotope enrichment also differentiates plant species based on familial identity. Differences in nitrogen concentrations clustered at the plant family level rather than degree of dependency on mycoheterotrophy.

• Conclusions We posit that these differences are related to plant family-specific physiological interactions with fungi and their environments.