The eighteenth-century natural histories of Paraquaria, a Jesuit province in South America ranging from the tropical forest to Río de la Plata (the River Plate), constitute a rich and consistent tradition of nature writing. The way the material is organized, the frequent use of lists of aboriginal names, and the focus on naming, all attest to the missionaries' preoccupation with language, understandable given that they were engaged in writing dictionaries and thesauri of the native tongues. During the nineteenth and twentieth centuries, this body of work went through a series of appropriations, reflecting the various intellectual programs that contributed to the making of the national tradition in Argentina. While these natural histories are still often interpreted in terms of Argentina's national history, science, and literature, I will argue that they should be considered a product of a mixed culture oriented toward the practical and religious goals that are characteristic of most of Jesuit missionary culture, the result of the missionaries' attempt at organizing their experience of the wilderness and their encounter with the aboriginal peoples.