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A hypothetical taxonomic tree. Nine Operational Taxonomic Units (OTUs) and four taxonomic levels are shown. For example, levels 1-4 could correspond to species, genera, families, and orders, respectively; in this case, species 1, 2, and 3 would belong to the same genus, species 1, 2, 3, and 4 to the same family, and so on. Taxonomic paths connecting taxa 1 and 5 (thick lines) and taxa 4 and 8 (dashed lines) are marked. See text for more details.
