Synallaxis omissa Hartert, 1901 was described as a species based on an adult female collected in Pará, Brazil. Hellmayr (1907) began treating the taxon as a subspecies of Synallaxis rutilans Temminck, 1823 although he considered it “similar in form to S. r. rutilans, but immediately distinguished by the lack of rufous in its plumage ...”. The subsequent authors maintained S. omissa as a subspecies, until Stopiglia et al (in prep.), based on molecular and morphological data, defended the validity of S. omissa as species. It is interesting to note that although all the main works have already mentioned S. omissa as a diagnosable taxon, it was considered a subspecies for more than a century. This can only be understood if one observes the historical context of the use of the trinominal nomenclature in bird taxonomy. In 1886 the AOU Code was published by the American Ornithologists’ Union. It remained in force for 75 years, until the ‘first’ edition of the ICZN Code was published in 1961. The bases of the AOU Code were those presented by the Strickland Code, but among its main changes was the “Principle of Trinomials”. Despite deep and heated discussions against the adoption of this principle by the European ornithological community, the use of the trinominal nomenclature in bird taxonomy has been constant since then. Being more imprecise than the already confusing species concept, the subspecies prevents the visualisation of natural units, especially in areas of mega diversity such as the Amazon, in addition to causing damage with respect to the direction of conservation actions. Synallaxis omissa is quite didactic in this respect, given the fact that although it is clearly distinctive taxon of one of the areas most threatened by loss of habitat of the whole Amazon, it has been neglected as a valid species and consequently is not part of the inventories of the global conservation status of animals (e.g. lists of threatened species). It was forgotten due to the shadows of the trinominal nomenclature.