Estimating how many species are yet to be known (that is, the extent of the so-called Linnean Shortfall) is particularly challenging. This is not only because there are many wild populations of new species yet to be discovered, or because some samples stored in Natural History collections are waiting to be studied. There are also many species to be discovered or synonymized (that is, degraded) in already known populations. In fact, species discoveries can come from splitting the populations of an already known species into two or more new species, thus increasing regional and global species checklists. And the populations some already recognized species will be lumped into larger species, thus loosing species from these checklists. Being species scientific hypotheses, they are subject to constant scrutiny and update, so these reclassifications are an integral part of the taxonomic process. In a perspective paper led by Thainá Lessa, we discuss the implications of this process for our ability to estimate the number of species yet to be discovered at regional and global scales.

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