ABSTRACT Uruguay occupies an area of special relevance for species of terrestrial orchids of the subtribe Spiranthinae because it is located in one of the largest continuous grassland regions of the Americas. The aim of this study is to provide a taxonomic study of Spiranthinae species from Uruguay. A total of 22 species distributed in seven genera were confirmed to the country, representing almost half of the species of terrestrial orchids in Uruguay. Cyclopogon (8 spp.), Skeptrostachys (5 spp.) and Brachystele (4 spp.) were the most representative. Additionally, a new synonym in Brachystele dilatata (=Brachystele waldemarii) is proposed. The group was found in all departments and ecoregions of the country, mainly in the southeastern (Maldonado: 10 spp., Rocha: 12 spp. Lavalleja: 10 spp.) and northeastern (Rivera: 11 spp., Tacuarembó 9 spp.) regions. Among the ecoregions, the “Serrano Forest” (17 spp.) and “Graben de la Laguna Merín” (14 spp.) were the most species-rich. Descriptions, illustrations, an identification key, and comments on geographical distribution of the species are provided.

Resumen Orchidaceae es una de las familias botánicas más estudiadas desde el punto de vista taxonómico y económico en el mundo. En Uruguay es poco conocida y los datos descriptivos que existen se encuentran fragmentados y dispersos. En este trabajo se presenta un inventario de la familia así como su distribución en ambientes, eco-regiones y departamentos del país basados en los registros de herbarios, publicaciones existentes y expediciones de campo realizadas durante el 2018-2019. Se presenta una lista con 59 especies en 18 géneros. Se encontraron cuatro especies endémicas de Uruguay, mientras que 22 spp. son endémicas del Cono Sur. La Cuenca Sedimentaria Gondwánica fue la eco-región en presentar mayor diversidad de especies (51%) y los departamentos con mayor riqueza fueron Cerro Largo (25 spp.) y Maldonado (25 spp.). Mientras que el Bosques Serranos y Bosque Ribereño fueron los más ricos en especies de orquídeas. Los géneros más representativos fueron Habenaria (12 spp.), Cyclopogon (8 spp.) y Brachystele (6 spp.) y las especies que presentaron distribución amplia fueron Habenaria gourlieana, H. parviflora, y Cyclopogon elatus, las cuales se encontraron en todas las eco-regiones y en 15 de los 19 departamentos del país.

Abstract From an economic and taxonomic point of view, Orchidaceae is one of the most studied botanical families. In Uruguay it is poorly represented and known, and descriptive data are fragmented and scattered. In the present work the information on the species of this family is updated based on herbaria records, previous publications and field trips made in the country during 2018-2019. A list of Orchidaceae from Uruguay is presented with 59 species belonging to18 genera. Four species were found endemic to the country, while 22 species are endemic to the Southern Cone region. The Gondwanic Sedimentary Basin was the ecoregion with the highest species diversity (51%) and the richest departments were Cerro Largo (25 spp.) and Maldonado (25 spp.). The Highland Forest and Riparian Forest environments presented highest diversity. The most representative genera were Habenaria (12 spp.), Cyclopogon (8 spp.), and Brachystele (6 spp.). The species with the widest distribution were Habenaria gourlieana, H. parviflora, and Cyclopogon elatus, which were found in all ecoregions and in 15 out of 19 departments of the country.