High species diversity, large area, and taxonomically under-studied groups are some of the explanations for the frequent discovery of new species of plants during ecological field campaigns in the Amazon region. Some of these new species are already being threatened from unplanned urban expansion associated with deforestation and habitat loss. Here we describe Tovomita cornuta, a new species discovered during ecological studies in the whitesand campinaranas of the Amazon, which is also threatened. The species is endemic to the state of Amazonas, Brazil, where it occurs in the understory of forested campinaranas physiognomies and is easily recognized by its narrowly obovoid fruits with dilated free styles. We provide a description, taxonomic and ecological comments, assessment of conservation status, geographic distribution, phenology, and illustrations for the new species.