Résumé
The Brachypodium distachyon complex includes three annual species, whose taxonomic identities have recently been demonstrated by cytological, molecular and morphological data. The initial taxonomic studies contained no nomenclatur-al revision of the twenty or so heterotypic synonyms at species rank, while the authors needed to describe two species as new. Indeed, the impossibility to study molecularly the herbarium type materials of these names precluded the analysis of these samples. An improvement of the morphological methods, including new criteria relevant both in situ and in herbar-ium, now allows us to do this nomenclatural synthesis, according to the current taxonomic treatment. Fresh French and Algerian materials from the three species have been calibrated with DNA genome size (2C) and molecular barcoding (ITS + tnrLF). We found that several valid previous names are available for B. stacei (whose distribution is more widespread than expected), of which Festuca rigida Roth is the older and yet has been used to combine Brachypodium rigidum (Roth) Link, the priority name of the species. Admissibility to propose a conservation or a rejection of one of these names is in debate. In order to fix their interpretation, nomenclatural types of a dozen other names will be designated at the end of this work, including lectotypes and neotypes. We found that the herbarium lectotype of Bromus distachyos L. (LINN93.48) corresponds to Brachypodium hybridum according to our current morphological analysis. In virtue of what a proposal to conserve and retypify the name Bromus distachyos L. could be a consensual solution in order to conserve the uses of both Bdistachyon and B. hybridum in their current senses. Field investigation also revealed other possible annual species of hybrid origin – at least one sensu Trachynia platystachya (Coss.) H. Scholz – but with an inversed parental combination than B. hybridum, which are currently investigated also genomically.