The circumscription of subtribe Calothecinae has undergone several changes since its description. Currently, three genera are considered in the subtribe: Chascolytrum, Laegaardia and Paramochloa, although no phylogenetic evidence for the placement of the two last genera was published so far. In this study we aim to evaluate the circumscription of Calothecinae and the infrageneric classification recently proposed for Chascolytrum using a more comprehensive sampling of taxa and molecular markers. We included species of all genera of Calothecinae, plus two South American species of Trisetum s.l. that have been suggested to be related to Chascolytrum, and representatives from subtribes Agrostidinae, Echinopogoninae, Brizinae, Torreyochloinae, Phalaridinae and Koeleriinae. We performed Bayesian and Maximum Likelihood analyses using a total of six molecular markers, including four plastid DNA regions (atpF-atpH, matK, rps16 intron, and trnL-trnF) and two ribosomal nuclear regions (ITS and ETS). Our results revealed that neither Calothecinae nor Chascolytrum are monophyletic considering their last circumscription. Trisetum brasiliense and T. bulbosum appeared nested to Chascolytrum, and are formally included in Calothecinae as incertae sedis. More studies are needed to confirm their taxonomic position. Based on morphological characters, Laegaardia and Paramochloa are transferred to the new subtribe Paramochloinae, and Chascolytrum is splitted in nine different genera, of which two are newly described: Boldrinia (gen. nov.), Calotheca, Chascolytrum, Erianthecium, Lombardochloa, Microbriza, Poidium, Rhombolytrum, and Rosengurttia (gen. nov.).

DNA data matrix from the concatenated Bayesian and Maximum Likelihood analyses.