Tetraglochin is distributed along the Andes from Peru to southern Argentina and central Chile. In order to test its monophyly and analyze relationships among species of this genus and allied genera, we conducted morphological studies and phylogenetic analyses using both nuclear (ITS) and cpDNA (trnL-F) sequences. As a result, Tetraglochin is supported as monophyletic, with the genus Margyricarpus as its sister group. Tetraglochin acanthocarpa and T. caespitosa are sister to the rest of the genus, which is grouped in two clades. One clade grows primarily distributed along the Central Andes, includes T. cristata, T. inermis, plus some specimens of T. ameghinoi, and has a coriaceous or papery and non translucent hypanthium. The other clade is mainly in the Southern Andes, contains T. alata and some specimens of T. ameghinoi, and has a membranous translucent hypanthium. Based on results obtained from morphological studies, molecular phylogenies, and species delimitation analyses, a new species T. andina, is proposed, segregated from T. ameghinoi. A key to identify all species herein recognized, and a map containing geographical distribution of them are provided, together with a description and illustration of the new species.