Closed reference clustering of OTUs and phylogenetic trees at different thresholds A results from the closed reference clustering of OTUs at each clustering threshold against composite LSU/ITS2 reference sequences. LSU matches in green, ITS2 matches in blue, linked matches (for which both an ITS2 and LSU OTU were matched to a reference sequence of the same species) in yellow. Underlined taxa indicate new matches at each clustering threshold B phylogenetic tree of LSU OTUs under increasingly stringent clustering thresholds, with arrows marking newly added taxa as threshold values are increased.