Calamagrostis perplexa is a New York State endemic grass species, hypothesized to be of hybrid origin, that previously was known only from a single locality. We provide a summary of its taxonomic history, report new New York records and ecological information for the taxon, and include a principal components analysis and key characterizing morphological variation in C. perplexa and its putative close relatives C. canadensis, C. porteri, C. rubescens, and C. scribneri. Calamagrostis perplexa is now known from two extant populations and a third population of unknown status; it remains a New York state endemic.