Order-level trees and splitting/lumping of OTUs at clustering A order-level ML trees with mixed OTU clustering thresholds (99% LSU D1-D2, 98% ITS2). Full tree in supplementary materials. Leotia lubrica was used as the outgroup (not pictured). Brackets indicate reference taxa linked to an ITS2 and/or LSU OTU, with colours indicating potential splitting/lumping (blue, splitting; green, lumping; orange, 1:1) B diagram illustrating the effects of splitting and lumping of an OTU in the fungal community on the tree inference. Four hypothetical species (A to D) in a community are treated under uniform clustering thresholds for ITS2 and LSU. This may result in deviation from the 1:1 ratio of OTUs expected if each species in the community is represented equally by both markers (species A). Threshold values may be too high, resulting in splitting of species into multiples OTUs, which is likely to affect the more variable ITS2 region (species B) or may be too low, resulting in lumping of multiple species into a single OTU, likely to affect the conservative LSU region (species C and D).